//  Linux/kernel/sched/fair.c
//  http://lxr.free-electrons.com/source/kernel/sched/fair.c?v=4.6
/*
 * Completely Fair Scheduling (CFS) Class (SCHED_NORMAL/SCHED_BATCH)
 *
 *  Copyright (C) 2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *
 *  Interactivity improvements by Mike Galbraith
 *  (C) 2007 Mike Galbraith <efault@gmx.de>
 *
 *  Various enhancements by Dmitry Adamushko.
 *  (C) 2007 Dmitry Adamushko <dmitry.adamushko@gmail.com>
 *
 *  Group scheduling enhancements by Srivatsa Vaddagiri
 *  Copyright IBM Corporation, 2007
 *  Author: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
 *
 *  Scaled math optimizations by Thomas Gleixner
 *  Copyright (C) 2007, Thomas Gleixner <tglx@linutronix.de>
 *
 *  Adaptive scheduling granularity, math enhancements by Peter Zijlstra
 *  Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
 */

#include <linux/sched.h>
#include <linux/latencytop.h>
#include <linux/cpumask.h>
#include <linux/cpuidle.h>
#include <linux/slab.h>
#include <linux/profile.h>
#include <linux/interrupt.h>
#include <linux/mempolicy.h>
#include <linux/migrate.h>
#include <linux/task_work.h>

#include <trace/events/sched.h>

#include "sched.h"

/*
 * Targeted preemption latency for CPU-bound tasks:
 * (default: 6ms * (1 + ilog(ncpus)), units: nanoseconds)
 *
 * NOTE: this latency value is not the same as the concept of
 * 'timeslice length' - timeslices in CFS are of variable length
 * and have no persistent notion like in traditional, time-slice
 * based scheduling concepts.
 *
 * (to see the precise effective timeslice length of your workload,
 *  run vmstat and monitor the context-switches (cs) field)
 */
unsigned int sysctl_sched_latency = 6000000ULL;
unsigned int normalized_sysctl_sched_latency = 6000000ULL;

/*
 * The initial- and re-scaling of tunables is configurable
 * (default SCHED_TUNABLESCALING_LOG = *(1+ilog(ncpus))
 *
 * Options are:
 * SCHED_TUNABLESCALING_NONE - unscaled, always *1
 * SCHED_TUNABLESCALING_LOG - scaled logarithmical, *1+ilog(ncpus)
 * SCHED_TUNABLESCALING_LINEAR - scaled linear, *ncpus
 */
enum sched_tunable_scaling sysctl_sched_tunable_scaling
    = SCHED_TUNABLESCALING_LOG;

/*
 * Minimal preemption granularity for CPU-bound tasks:
 * (default: 0.75 msec * (1 + ilog(ncpus)), units: nanoseconds)
 */
unsigned int sysctl_sched_min_granularity = 750000ULL;
unsigned int normalized_sysctl_sched_min_granularity = 750000ULL;

/*
 * is kept at sysctl_sched_latency / sysctl_sched_min_granularity
 */
static unsigned int sched_nr_latency = 8;

/*
 * After fork, child runs first. If set to 0 (default) then
 * parent will (try to) run first.
 */
unsigned int sysctl_sched_child_runs_first __read_mostly;

/*
 * SCHED_OTHER wake-up granularity.
 * (default: 1 msec * (1 + ilog(ncpus)), units: nanoseconds)
 *
 * This option delays the preemption effects of decoupled workloads
 * and reduces their over-scheduling. Synchronous workloads will still
 * have immediate wakeup/sleep latencies.
 */
unsigned int sysctl_sched_wakeup_granularity = 1000000UL;
unsigned int normalized_sysctl_sched_wakeup_granularity = 1000000UL;

const_debug unsigned int sysctl_sched_migration_cost = 500000UL;

/*
 * The exponential sliding  window over which load is averaged for shares
 * distribution.
 * (default: 10msec)
 */
unsigned int __read_mostly sysctl_sched_shares_window = 10000000UL;

#ifdef CONFIG_CFS_BANDWIDTH
/*
 * Amount of runtime to allocate from global (tg) to local (per-cfs_rq) pool
 * each time a cfs_rq requests quota.
 *
 * Note: in the case that the slice exceeds the runtime remaining (either due
 * to consumption or the quota being specified to be smaller than the slice)
 * we will always only issue the remaining available time.
 *
 * default: 5 msec, units: microseconds
  */
unsigned int sysctl_sched_cfs_bandwidth_slice = 5000UL;
#endif

static inline void update_load_add(struct load_weight *lw, unsigned long inc)
{
    lw->weight += inc;
    lw->inv_weight = 0;
}

static inline void update_load_sub(struct load_weight *lw, unsigned long dec)
{
    lw->weight -= dec;
    lw->inv_weight = 0;
}

static inline void update_load_set(struct load_weight *lw, unsigned long w)
{
    lw->weight = w;
    lw->inv_weight = 0;
}

/*
 * Increase the granularity value when there are more CPUs,
 * because with more CPUs the 'effective latency' as visible
 * to users decreases. But the relationship is not linear,
 * so pick a second-best guess by going with the log2 of the
 * number of CPUs.
 *
 * This idea comes from the SD scheduler of Con Kolivas:
 */
static unsigned int get_update_sysctl_factor(void)
{
    unsigned int cpus = min_t(unsigned int, num_online_cpus(), 8);
    unsigned int factor;

    switch (sysctl_sched_tunable_scaling) {
    case SCHED_TUNABLESCALING_NONE:
        factor = 1;
        break;
    case SCHED_TUNABLESCALING_LINEAR:
        factor = cpus;
        break;
    case SCHED_TUNABLESCALING_LOG:
    default:
        factor = 1 + ilog2(cpus);
        break;
    }

    return factor;
}

static void update_sysctl(void)
{
    unsigned int factor = get_update_sysctl_factor();

#define SET_SYSCTL(name) \
    (sysctl_##name = (factor) * normalized_sysctl_##name)
    SET_SYSCTL(sched_min_granularity);
    SET_SYSCTL(sched_latency);
    SET_SYSCTL(sched_wakeup_granularity);
#undef SET_SYSCTL
}

void sched_init_granularity(void)
{
    update_sysctl();
}

#define WMULT_CONST     (~0U)
#define WMULT_SHIFT     32

static void __update_inv_weight(struct load_weight *lw)
{
    unsigned long w;

    if (likely(lw->inv_weight))
        return;

    w = scale_load_down(lw->weight);

    if (BITS_PER_LONG > 32 && unlikely(w >= WMULT_CONST))
        lw->inv_weight = 1;
    else if (unlikely(!w))
        lw->inv_weight = WMULT_CONST;
    else
        lw->inv_weight = WMULT_CONST / w;
}

/*
 * delta_exec * weight / lw.weight
 *   OR
 * (delta_exec * (weight * lw->inv_weight)) >> WMULT_SHIFT
 *
 * Either weight := NICE_0_LOAD and lw \e prio_to_wmult[], in which case
 * we're guaranteed shift stays positive because inv_weight is guaranteed to
 * fit 32 bits, and NICE_0_LOAD gives another 10 bits; therefore shift >= 22.
 *
 * Or, weight =< lw.weight (because lw.weight is the runqueue weight), thus
 * weight/lw.weight <= 1, and therefore our shift will also be positive.
 */
static u64 __calc_delta(u64 delta_exec, unsigned long weight, struct load_weight *lw)
{
    u64 fact = scale_load_down(weight);
    int shift = WMULT_SHIFT;

    __update_inv_weight(lw);

    if (unlikely(fact >> 32)) {
        while (fact >> 32) {
            fact >>= 1;
            shift--;
        }
    }

    /* hint to use a 32x32->64 mul */
    fact = (u64)(u32)fact * lw->inv_weight;

    while (fact >> 32) {
        fact >>= 1;
        shift--;
    }

    return mul_u64_u32_shr(delta_exec, fact, shift);
}


const struct sched_class fair_sched_class;

/**************************************************************
 * CFS operations on generic schedulable entities:
 */

#ifdef CONFIG_FAIR_GROUP_SCHED

/* cpu runqueue to which this cfs_rq is attached */
static inline struct rq *rq_of(struct cfs_rq *cfs_rq)
{
    return cfs_rq->rq;
}

/* An entity is a task if it doesn't "own" a runqueue */
#define entity_is_task(se)      (!se->my_q)

static inline struct task_struct *task_of(struct sched_entity *se)
{
#ifdef CONFIG_SCHED_DEBUG
    WARN_ON_ONCE(!entity_is_task(se));
#endif
    return container_of(se, struct task_struct, se);
}

/* Walk up scheduling entities hierarchy */
#define for_each_sched_entity(se) \
        for (; se; se = se->parent)

static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
{
    return p->se.cfs_rq;
}

/* runqueue on which this entity is (to be) queued */
static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
{
    return se->cfs_rq;
}

/* runqueue "owned" by this group */
static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
{
    return grp->my_q;
}

static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
    if (!cfs_rq->on_list) {
        /*
         * Ensure we either appear before our parent (if already
         * enqueued) or force our parent to appear after us when it is
         * enqueued.  The fact that we always enqueue bottom-up
         * reduces this to two cases.
         */
        if (cfs_rq->tg->parent &&
            cfs_rq->tg->parent->cfs_rq[cpu_of(rq_of(cfs_rq))]->on_list) {
            list_add_rcu(&cfs_rq->leaf_cfs_rq_list,
                &rq_of(cfs_rq)->leaf_cfs_rq_list);
        } else {
            list_add_tail_rcu(&cfs_rq->leaf_cfs_rq_list,
                &rq_of(cfs_rq)->leaf_cfs_rq_list);
        }

        cfs_rq->on_list = 1;
    }
}

static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
    if (cfs_rq->on_list) {
        list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
        cfs_rq->on_list = 0;
    }
}

/* Iterate thr' all leaf cfs_rq's on a runqueue */
#define for_each_leaf_cfs_rq(rq, cfs_rq) \
    list_for_each_entry_rcu(cfs_rq, &rq->leaf_cfs_rq_list, leaf_cfs_rq_list)

/* Do the two (enqueued) entities belong to the same group ? */
static inline struct cfs_rq *
is_same_group(struct sched_entity *se, struct sched_entity *pse)
{
    if (se->cfs_rq == pse->cfs_rq)
        return se->cfs_rq;

    return NULL;
}

static inline struct sched_entity *parent_entity(struct sched_entity *se)
{
    return se->parent;
}

static void
find_matching_se(struct sched_entity **se, struct sched_entity **pse)
{
    int se_depth, pse_depth;

    /*
     * preemption test can be made between sibling entities who are in the
     * same cfs_rq i.e who have a common parent. Walk up the hierarchy of
     * both tasks until we find their ancestors who are siblings of common
     * parent.
     */

    /* First walk up until both entities are at same depth */
    se_depth = (*se)->depth;
    pse_depth = (*pse)->depth;

    while (se_depth > pse_depth) {
        se_depth--;
        *se = parent_entity(*se);
    }

    while (pse_depth > se_depth) {
        pse_depth--;
        *pse = parent_entity(*pse);
    }

    while (!is_same_group(*se, *pse)) {
        *se = parent_entity(*se);
        *pse = parent_entity(*pse);
    }
}

#else   /* !CONFIG_FAIR_GROUP_SCHED */

static inline struct task_struct *task_of(struct sched_entity *se)
{
    return container_of(se, struct task_struct, se);
}

static inline struct rq *rq_of(struct cfs_rq *cfs_rq)
{
    return container_of(cfs_rq, struct rq, cfs);
}

#define entity_is_task(se)      1

#define for_each_sched_entity(se) \
        for (; se; se = NULL)

static inline struct cfs_rq *task_cfs_rq(struct task_struct *p)
{
    return &task_rq(p)->cfs;
}

static inline struct cfs_rq *cfs_rq_of(struct sched_entity *se)
{
    struct task_struct *p = task_of(se);
    struct rq *rq = task_rq(p);

    return &rq->cfs;
}

/* runqueue "owned" by this group */
static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp)
{
    return NULL;
}

static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
}

static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
}

#define for_each_leaf_cfs_rq(rq, cfs_rq) \
        for (cfs_rq = &rq->cfs; cfs_rq; cfs_rq = NULL)

static inline struct sched_entity *parent_entity(struct sched_entity *se)
{
    return NULL;
}

static inline void
find_matching_se(struct sched_entity **se, struct sched_entity **pse)
{
}

#endif  /* CONFIG_FAIR_GROUP_SCHED */

static __always_inline
void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec);

/**************************************************************
 * Scheduling class tree data structure manipulation methods:
 */

static inline u64 max_vruntime(u64 max_vruntime, u64 vruntime)
{
    s64 delta = (s64)(vruntime - max_vruntime);
    if (delta > 0)
        max_vruntime = vruntime;

    return max_vruntime;
}

static inline u64 min_vruntime(u64 min_vruntime, u64 vruntime)
{
    s64 delta = (s64)(vruntime - min_vruntime);
    if (delta < 0)
        min_vruntime = vruntime;

    return min_vruntime;
}

static inline int entity_before(struct sched_entity *a,
                struct sched_entity *b)
{
    return (s64)(a->vruntime - b->vruntime) < 0;
}

static void update_min_vruntime(struct cfs_rq *cfs_rq)
{
    u64 vruntime = cfs_rq->min_vruntime;

    if (cfs_rq->curr)
        vruntime = cfs_rq->curr->vruntime;

    if (cfs_rq->rb_leftmost) {
        struct sched_entity *se = rb_entry(cfs_rq->rb_leftmost,
                           struct sched_entity,
                           run_node);

        if (!cfs_rq->curr)
            vruntime = se->vruntime;
        else
            vruntime = min_vruntime(vruntime, se->vruntime);
    }

    /* ensure we never gain time by being placed backwards. */
    cfs_rq->min_vruntime = max_vruntime(cfs_rq->min_vruntime, vruntime);
#ifndef CONFIG_64BIT
    smp_wmb();
    cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
#endif
}

/*
 * Enqueue an entity into the rb-tree:
 */
static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    struct rb_node **link = &cfs_rq->tasks_timeline.rb_node;
    struct rb_node *parent = NULL;
    struct sched_entity *entry;
    int leftmost = 1;

    /*
     * Find the right place in the rbtree:
     * 从红黑树中找到se所应该在的位置
     * 同时leftmost标识其位置是不是最左结点
     * 如果在查找结点的过程中向右走了, 则置leftmost为0
     * 否则说明一直再相左走, 最终将走到最左节点, 此时leftmost恒为1
     */
    while (*link) {
        parent = *link;
        entry = rb_entry(parent, struct sched_entity, run_node);
        /*
         * We dont care about collisions. Nodes with
         * the same key stay together.
         * 以se->vruntime值为键值进行红黑树结点的比较
         */
        if (entity_before(se, entry)) {
            link = &parent->rb_left;
        } else {
            link = &parent->rb_right;
            leftmost = 0;
        }
    }
    /*
     * Maintain a cache of leftmost tree entries (it is frequently
     * used):
     * 如果leftmost为1, 说明se是红黑树当前的最左结点, 即vruntime最小
     * 那么把这个节点保存在cfs就绪队列的rb_leftmost域中
     */
    if (leftmost)
        cfs_rq->rb_leftmost = &se->run_node;

    /*  将新进程的节点加入到红黑树中  */
    rb_link_node(&se->run_node, parent, link);
    /*  为新插入的结点进行着色  */
    rb_insert_color(&se->run_node, &cfs_rq->tasks_timeline);
}

static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    if (cfs_rq->rb_leftmost == &se->run_node) {
        struct rb_node *next_node;

        next_node = rb_next(&se->run_node);
        cfs_rq->rb_leftmost = next_node;
    }

    rb_erase(&se->run_node, &cfs_rq->tasks_timeline);
}

struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
{
    struct rb_node *left = cfs_rq->rb_leftmost;

    if (!left)
        return NULL;

    return rb_entry(left, struct sched_entity, run_node);
}

static struct sched_entity *__pick_next_entity(struct sched_entity *se)
{
    struct rb_node *next = rb_next(&se->run_node);

    if (!next)
        return NULL;

    return rb_entry(next, struct sched_entity, run_node);
}

#ifdef CONFIG_SCHED_DEBUG
struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
{
    struct rb_node *last = rb_last(&cfs_rq->tasks_timeline);

    if (!last)
        return NULL;

    return rb_entry(last, struct sched_entity, run_node);
}

/**************************************************************
 * Scheduling class statistics methods:
 */

int sched_proc_update_handler(struct ctl_table *table, int write,
        void __user *buffer, size_t *lenp,
        loff_t *ppos)
{
    int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
    unsigned int factor = get_update_sysctl_factor();

    if (ret || !write)
        return ret;

    sched_nr_latency = DIV_ROUND_UP(sysctl_sched_latency,
                    sysctl_sched_min_granularity);

#define WRT_SYSCTL(name) \
    (normalized_sysctl_##name = sysctl_##name / (factor))
    WRT_SYSCTL(sched_min_granularity);
    WRT_SYSCTL(sched_latency);
    WRT_SYSCTL(sched_wakeup_granularity);
#undef WRT_SYSCTL

    return 0;
}
#endif

/*
 * delta /= w
 */
static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
{
    if (unlikely(se->load.weight != NICE_0_LOAD))
        delta = __calc_delta(delta, NICE_0_LOAD, &se->load);

    return delta;
}

/*
 * The idea is to set a period in which each task runs once.
 *
 * When there are too many tasks (sched_nr_latency) we have to stretch
 * this period because otherwise the slices get too small.
 *
 * p = (nr <= nl) ? l : l*nr/nl
 */
static u64 __sched_period(unsigned long nr_running)
{
    if (unlikely(nr_running > sched_nr_latency))
        return nr_running * sysctl_sched_min_granularity;
    else
        return sysctl_sched_latency;
}

/*
 * We calculate the wall-time slice from the period by taking a part
 * proportional to the weight.
 *
 * s = p*P[w/rw]
 */
static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    u64 slice = __sched_period(cfs_rq->nr_running + !se->on_rq);

    for_each_sched_entity(se) {
        struct load_weight *load;
        struct load_weight lw;

        cfs_rq = cfs_rq_of(se);
        load = &cfs_rq->load;

        if (unlikely(!se->on_rq)) {
            lw = cfs_rq->load;

            update_load_add(&lw, se->load.weight);
            load = &lw;
        }
        slice = __calc_delta(slice, se->load.weight, load);
    }
    return slice;
}

/*
 * We calculate the vruntime slice of a to-be-inserted task.
 *
 * vs = s/w
 */
static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    return calc_delta_fair(sched_slice(cfs_rq, se), se);
}

#ifdef CONFIG_SMP
static int select_idle_sibling(struct task_struct *p, int cpu);
static unsigned long task_h_load(struct task_struct *p);

/*
 * We choose a half-life close to 1 scheduling period.
 * Note: The tables runnable_avg_yN_inv and runnable_avg_yN_sum are
 * dependent on this value.
 */
#define LOAD_AVG_PERIOD 32
#define LOAD_AVG_MAX 47742 /* maximum possible load avg */
#define LOAD_AVG_MAX_N 345 /* number of full periods to produce LOAD_AVG_MAX */

/* Give new sched_entity start runnable values to heavy its load in infant time */
void init_entity_runnable_average(struct sched_entity *se)
{
    struct sched_avg *sa = &se->avg;

    sa->last_update_time = 0;
    /*
     * sched_avg's period_contrib should be strictly less then 1024, so
     * we give it 1023 to make sure it is almost a period (1024us), and
     * will definitely be update (after enqueue).
     */
    sa->period_contrib = 1023;
    sa->load_avg = scale_load_down(se->load.weight);
    sa->load_sum = sa->load_avg * LOAD_AVG_MAX;
    sa->util_avg = scale_load_down(SCHED_LOAD_SCALE);
    sa->util_sum = sa->util_avg * LOAD_AVG_MAX;
    /* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */
}

static inline unsigned long cfs_rq_runnable_load_avg(struct cfs_rq *cfs_rq);
static inline unsigned long cfs_rq_load_avg(struct cfs_rq *cfs_rq);
#else
void init_entity_runnable_average(struct sched_entity *se)
{
}
#endif

/*
 * Update the current task's runtime statistics.
 */
static void update_curr(struct cfs_rq *cfs_rq)
{
    struct sched_entity *curr = cfs_rq->curr;
    u64 now = rq_clock_task(rq_of(cfs_rq));
    u64 delta_exec;

    if (unlikely(!curr))
        return;

    delta_exec = now - curr->exec_start;
    if (unlikely((s64)delta_exec <= 0))
        return;

    curr->exec_start = now;

    schedstat_set(curr->statistics.exec_max,
              max(delta_exec, curr->statistics.exec_max));

    curr->sum_exec_runtime += delta_exec;
    schedstat_add(cfs_rq, exec_clock, delta_exec);

    curr->vruntime += calc_delta_fair(delta_exec, curr);
    update_min_vruntime(cfs_rq);

    if (entity_is_task(curr)) {
        struct task_struct *curtask = task_of(curr);

        trace_sched_stat_runtime(curtask, delta_exec, curr->vruntime);
        cpuacct_charge(curtask, delta_exec);
        account_group_exec_runtime(curtask, delta_exec);
    }

    account_cfs_rq_runtime(cfs_rq, delta_exec);
}

static void update_curr_fair(struct rq *rq)
{
    update_curr(cfs_rq_of(&rq->curr->se));
}

#ifdef CONFIG_SCHEDSTATS
static inline void
update_stats_wait_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    u64 wait_start = rq_clock(rq_of(cfs_rq));

    if (entity_is_task(se) && task_on_rq_migrating(task_of(se)) &&
        likely(wait_start > se->statistics.wait_start))
        wait_start -= se->statistics.wait_start;

    se->statistics.wait_start = wait_start;
}

static void
update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    struct task_struct *p;
    u64 delta;

    delta = rq_clock(rq_of(cfs_rq)) - se->statistics.wait_start;

    if (entity_is_task(se)) {
        p = task_of(se);
        if (task_on_rq_migrating(p)) {
            /*
             * Preserve migrating task's wait time so wait_start
             * time stamp can be adjusted to accumulate wait time
             * prior to migration.
             */
            se->statistics.wait_start = delta;
            return;
        }
        trace_sched_stat_wait(p, delta);
    }

    se->statistics.wait_max = max(se->statistics.wait_max, delta);
    se->statistics.wait_count++;
    se->statistics.wait_sum += delta;
    se->statistics.wait_start = 0;
}

/*
 * Task is being enqueued - update stats:
 */
static inline void
update_stats_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    /*
     * Are we enqueueing a waiting task? (for current tasks
     * a dequeue/enqueue event is a NOP)
     */
    if (se != cfs_rq->curr)
        update_stats_wait_start(cfs_rq, se);
}

static inline void
update_stats_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
    /*
     * Mark the end of the wait period if dequeueing a
     * waiting task:
     */
    if (se != cfs_rq->curr)
        update_stats_wait_end(cfs_rq, se);

    if (flags & DEQUEUE_SLEEP) {
        if (entity_is_task(se)) {
            struct task_struct *tsk = task_of(se);

            if (tsk->state & TASK_INTERRUPTIBLE)
                se->statistics.sleep_start = rq_clock(rq_of(cfs_rq));
            if (tsk->state & TASK_UNINTERRUPTIBLE)
                se->statistics.block_start = rq_clock(rq_of(cfs_rq));
        }
    }

}
#else
static inline void
update_stats_wait_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
}

static inline void
update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
}

static inline void
update_stats_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
}

static inline void
update_stats_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
}
#endif

/*
 * We are picking a new current task - update its stats:
 */
static inline void
update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    /*
     * We are starting a new run period:
     */
    se->exec_start = rq_clock_task(rq_of(cfs_rq));
}

/**************************************************
 * Scheduling class queueing methods:
 */

#ifdef CONFIG_NUMA_BALANCING
/*
 * Approximate time to scan a full NUMA task in ms. The task scan period is
 * calculated based on the tasks virtual memory size and
 * numa_balancing_scan_size.
 */
unsigned int sysctl_numa_balancing_scan_period_min = 1000;
unsigned int sysctl_numa_balancing_scan_period_max = 60000;

/* Portion of address space to scan in MB */
unsigned int sysctl_numa_balancing_scan_size = 256;

/* Scan @scan_size MB every @scan_period after an initial @scan_delay in ms */
unsigned int sysctl_numa_balancing_scan_delay = 1000;

static unsigned int task_nr_scan_windows(struct task_struct *p)
{
    unsigned long rss = 0;
    unsigned long nr_scan_pages;

    /*
     * Calculations based on RSS as non-present and empty pages are skipped
     * by the PTE scanner and NUMA hinting faults should be trapped based
     * on resident pages
     */
    nr_scan_pages = sysctl_numa_balancing_scan_size << (20 - PAGE_SHIFT);
    rss = get_mm_rss(p->mm);
    if (!rss)
        rss = nr_scan_pages;

    rss = round_up(rss, nr_scan_pages);
    return rss / nr_scan_pages;
}

/* For sanitys sake, never scan more PTEs than MAX_SCAN_WINDOW MB/sec. */
#define MAX_SCAN_WINDOW 2560

static unsigned int task_scan_min(struct task_struct *p)
{
    unsigned int scan_size = READ_ONCE(sysctl_numa_balancing_scan_size);
    unsigned int scan, floor;
    unsigned int windows = 1;

    if (scan_size < MAX_SCAN_WINDOW)
        windows = MAX_SCAN_WINDOW / scan_size;
    floor = 1000 / windows;

    scan = sysctl_numa_balancing_scan_period_min / task_nr_scan_windows(p);
    return max_t(unsigned int, floor, scan);
}

static unsigned int task_scan_max(struct task_struct *p)
{
    unsigned int smin = task_scan_min(p);
    unsigned int smax;

    /* Watch for min being lower than max due to floor calculations */
    smax = sysctl_numa_balancing_scan_period_max / task_nr_scan_windows(p);
    return max(smin, smax);
}

static void account_numa_enqueue(struct rq *rq, struct task_struct *p)
{
    rq->nr_numa_running += (p->numa_preferred_nid != -1);
    rq->nr_preferred_running += (p->numa_preferred_nid == task_node(p));
}

static void account_numa_dequeue(struct rq *rq, struct task_struct *p)
{
    rq->nr_numa_running -= (p->numa_preferred_nid != -1);
    rq->nr_preferred_running -= (p->numa_preferred_nid == task_node(p));
}

struct numa_group {
    atomic_t refcount;

    spinlock_t lock; /* nr_tasks, tasks */
    int nr_tasks;
    pid_t gid;
    int active_nodes;

    struct rcu_head rcu;
    unsigned long total_faults;
    unsigned long max_faults_cpu;
    /*
     * Faults_cpu is used to decide whether memory should move
     * towards the CPU. As a consequence, these stats are weighted
     * more by CPU use than by memory faults.
     */
    unsigned long *faults_cpu;
    unsigned long faults[0];
};

/* Shared or private faults. */
#define NR_NUMA_HINT_FAULT_TYPES 2

/* Memory and CPU locality */
#define NR_NUMA_HINT_FAULT_STATS (NR_NUMA_HINT_FAULT_TYPES * 2)

/* Averaged statistics, and temporary buffers. */
#define NR_NUMA_HINT_FAULT_BUCKETS (NR_NUMA_HINT_FAULT_STATS * 2)

pid_t task_numa_group_id(struct task_struct *p)
{
    return p->numa_group ? p->numa_group->gid : 0;
}

/*
 * The averaged statistics, shared & private, memory & cpu,
 * occupy the first half of the array. The second half of the
 * array is for current counters, which are averaged into the
 * first set by task_numa_placement.
 */
static inline int task_faults_idx(enum numa_faults_stats s, int nid, int priv)
{
    return NR_NUMA_HINT_FAULT_TYPES * (s * nr_node_ids + nid) + priv;
}

static inline unsigned long task_faults(struct task_struct *p, int nid)
{
    if (!p->numa_faults)
        return 0;

    return p->numa_faults[task_faults_idx(NUMA_MEM, nid, 0)] +
        p->numa_faults[task_faults_idx(NUMA_MEM, nid, 1)];
}

static inline unsigned long group_faults(struct task_struct *p, int nid)
{
    if (!p->numa_group)
        return 0;

    return p->numa_group->faults[task_faults_idx(NUMA_MEM, nid, 0)] +
        p->numa_group->faults[task_faults_idx(NUMA_MEM, nid, 1)];
}

static inline unsigned long group_faults_cpu(struct numa_group *group, int nid)
{
    return group->faults_cpu[task_faults_idx(NUMA_MEM, nid, 0)] +
        group->faults_cpu[task_faults_idx(NUMA_MEM, nid, 1)];
}

/*
 * A node triggering more than 1/3 as many NUMA faults as the maximum is
 * considered part of a numa group's pseudo-interleaving set. Migrations
 * between these nodes are slowed down, to allow things to settle down.
 */
#define ACTIVE_NODE_FRACTION 3

static bool numa_is_active_node(int nid, struct numa_group *ng)
{
    return group_faults_cpu(ng, nid) * ACTIVE_NODE_FRACTION > ng->max_faults_cpu;
}

/* Handle placement on systems where not all nodes are directly connected. */
static unsigned long score_nearby_nodes(struct task_struct *p, int nid,
                    int maxdist, bool task)
{
    unsigned long score = 0;
    int node;

    /*
     * All nodes are directly connected, and the same distance
     * from each other. No need for fancy placement algorithms.
     */
    if (sched_numa_topology_type == NUMA_DIRECT)
        return 0;

    /*
     * This code is called for each node, introducing N^2 complexity,
     * which should be ok given the number of nodes rarely exceeds 8.
     */
    for_each_online_node(node) {
        unsigned long faults;
        int dist = node_distance(nid, node);

        /*
         * The furthest away nodes in the system are not interesting
         * for placement; nid was already counted.
         */
        if (dist == sched_max_numa_distance || node == nid)
            continue;

        /*
         * On systems with a backplane NUMA topology, compare groups
         * of nodes, and move tasks towards the group with the most
         * memory accesses. When comparing two nodes at distance
         * "hoplimit", only nodes closer by than "hoplimit" are part
         * of each group. Skip other nodes.
         */
        if (sched_numa_topology_type == NUMA_BACKPLANE &&
                    dist > maxdist)
            continue;

        /* Add up the faults from nearby nodes. */
        if (task)
            faults = task_faults(p, node);
        else
            faults = group_faults(p, node);

        /*
         * On systems with a glueless mesh NUMA topology, there are
         * no fixed "groups of nodes". Instead, nodes that are not
         * directly connected bounce traffic through intermediate
         * nodes; a numa_group can occupy any set of nodes.
         * The further away a node is, the less the faults count.
         * This seems to result in good task placement.
         */
        if (sched_numa_topology_type == NUMA_GLUELESS_MESH) {
            faults *= (sched_max_numa_distance - dist);
            faults /= (sched_max_numa_distance - LOCAL_DISTANCE);
        }

        score += faults;
    }

    return score;
}

/*
 * These return the fraction of accesses done by a particular task, or
 * task group, on a particular numa node.  The group weight is given a
 * larger multiplier, in order to group tasks together that are almost
 * evenly spread out between numa nodes.
 */
static inline unsigned long task_weight(struct task_struct *p, int nid,
                    int dist)
{
    unsigned long faults, total_faults;

    if (!p->numa_faults)
        return 0;

    total_faults = p->total_numa_faults;

    if (!total_faults)
        return 0;

    faults = task_faults(p, nid);
    faults += score_nearby_nodes(p, nid, dist, true);

    return 1000 * faults / total_faults;
}

static inline unsigned long group_weight(struct task_struct *p, int nid,
                     int dist)
{
    unsigned long faults, total_faults;

    if (!p->numa_group)
        return 0;

    total_faults = p->numa_group->total_faults;

    if (!total_faults)
        return 0;

    faults = group_faults(p, nid);
    faults += score_nearby_nodes(p, nid, dist, false);

    return 1000 * faults / total_faults;
}

bool should_numa_migrate_memory(struct task_struct *p, struct page * page,
                int src_nid, int dst_cpu)
{
    struct numa_group *ng = p->numa_group;
    int dst_nid = cpu_to_node(dst_cpu);
    int last_cpupid, this_cpupid;

    this_cpupid = cpu_pid_to_cpupid(dst_cpu, current->pid);

    /*
     * Multi-stage node selection is used in conjunction with a periodic
     * migration fault to build a temporal task<->page relation. By using
     * a two-stage filter we remove short/unlikely relations.
     *
     * Using P(p) ~ n_p / n_t as per frequentist probability, we can equate
     * a task's usage of a particular page (n_p) per total usage of this
     * page (n_t) (in a given time-span) to a probability.
     *
     * Our periodic faults will sample this probability and getting the
     * same result twice in a row, given these samples are fully
     * independent, is then given by P(n)^2, provided our sample period
     * is sufficiently short compared to the usage pattern.
     *
     * This quadric squishes small probabilities, making it less likely we
     * act on an unlikely task<->page relation.
     */
    last_cpupid = page_cpupid_xchg_last(page, this_cpupid);
    if (!cpupid_pid_unset(last_cpupid) &&
                cpupid_to_nid(last_cpupid) != dst_nid)
        return false;

    /* Always allow migrate on private faults */
    if (cpupid_match_pid(p, last_cpupid))
        return true;

    /* A shared fault, but p->numa_group has not been set up yet. */
    if (!ng)
        return true;

    /*
     * Destination node is much more heavily used than the source
     * node? Allow migration.
     */
    if (group_faults_cpu(ng, dst_nid) > group_faults_cpu(ng, src_nid) *
                    ACTIVE_NODE_FRACTION)
        return true;

    /*
     * Distribute memory according to CPU & memory use on each node,
     * with 3/4 hysteresis to avoid unnecessary memory migrations:
     *
     * faults_cpu(dst)   3   faults_cpu(src)
     * --------------- * - > ---------------
     * faults_mem(dst)   4   faults_mem(src)
     */
    return group_faults_cpu(ng, dst_nid) * group_faults(p, src_nid) * 3 >
           group_faults_cpu(ng, src_nid) * group_faults(p, dst_nid) * 4;
}

static unsigned long weighted_cpuload(const int cpu);
static unsigned long source_load(int cpu, int type);
static unsigned long target_load(int cpu, int type);
static unsigned long capacity_of(int cpu);
static long effective_load(struct task_group *tg, int cpu, long wl, long wg);

/* Cached statistics for all CPUs within a node */
struct numa_stats {
    unsigned long nr_running;
    unsigned long load;

    /* Total compute capacity of CPUs on a node */
    unsigned long compute_capacity;

    /* Approximate capacity in terms of runnable tasks on a node */
    unsigned long task_capacity;
    int has_free_capacity;
};

/*
 * XXX borrowed from update_sg_lb_stats
 */
static void update_numa_stats(struct numa_stats *ns, int nid)
{
    int smt, cpu, cpus = 0;
    unsigned long capacity;

    memset(ns, 0, sizeof(*ns));
    for_each_cpu(cpu, cpumask_of_node(nid)) {
        struct rq *rq = cpu_rq(cpu);

        ns->nr_running += rq->nr_running;
        ns->load += weighted_cpuload(cpu);
        ns->compute_capacity += capacity_of(cpu);

        cpus++;
    }

    /*
     * If we raced with hotplug and there are no CPUs left in our mask
     * the @ns structure is NULL'ed and task_numa_compare() will
     * not find this node attractive.
     *
     * We'll either bail at !has_free_capacity, or we'll detect a huge
     * imbalance and bail there.
     */
    if (!cpus)
        return;

    /* smt := ceil(cpus / capacity), assumes: 1 < smt_power < 2 */
    smt = DIV_ROUND_UP(SCHED_CAPACITY_SCALE * cpus, ns->compute_capacity);
    capacity = cpus / smt; /* cores */

    ns->task_capacity = min_t(unsigned, capacity,
        DIV_ROUND_CLOSEST(ns->compute_capacity, SCHED_CAPACITY_SCALE));
    ns->has_free_capacity = (ns->nr_running < ns->task_capacity);
}

struct task_numa_env {
    struct task_struct *p;

    int src_cpu, src_nid;
    int dst_cpu, dst_nid;

    struct numa_stats src_stats, dst_stats;

    int imbalance_pct;
    int dist;

    struct task_struct *best_task;
    long best_imp;
    int best_cpu;
};

static void task_numa_assign(struct task_numa_env *env,
                 struct task_struct *p, long imp)
{
    if (env->best_task)
        put_task_struct(env->best_task);

    env->best_task = p;
    env->best_imp = imp;
    env->best_cpu = env->dst_cpu;
}

static bool load_too_imbalanced(long src_load, long dst_load,
                struct task_numa_env *env)
{
    long imb, old_imb;
    long orig_src_load, orig_dst_load;
    long src_capacity, dst_capacity;

    /*
     * The load is corrected for the CPU capacity available on each node.
     *
     * src_load    dst_load
     * ------------ vs ---------
     * src_capacity    dst_capacity
     */
    src_capacity = env->src_stats.compute_capacity;
    dst_capacity = env->dst_stats.compute_capacity;

    /* We care about the slope of the imbalance, not the direction. */
    if (dst_load < src_load)
        swap(dst_load, src_load);

    /* Is the difference below the threshold? */
    imb = dst_load * src_capacity * 100 -
          src_load * dst_capacity * env->imbalance_pct;
    if (imb <= 0)
        return false;

    /*
     * The imbalance is above the allowed threshold.
     * Compare it with the old imbalance.
     */
    orig_src_load = env->src_stats.load;
    orig_dst_load = env->dst_stats.load;

    if (orig_dst_load < orig_src_load)
        swap(orig_dst_load, orig_src_load);

    old_imb = orig_dst_load * src_capacity * 100 -
          orig_src_load * dst_capacity * env->imbalance_pct;

    /* Would this change make things worse? */
    return (imb > old_imb);
}

/*
 * This checks if the overall compute and NUMA accesses of the system would
 * be improved if the source tasks was migrated to the target dst_cpu taking
 * into account that it might be best if task running on the dst_cpu should
 * be exchanged with the source task
 */
static void task_numa_compare(struct task_numa_env *env,
                  long taskimp, long groupimp)
{
    struct rq *src_rq = cpu_rq(env->src_cpu);
    struct rq *dst_rq = cpu_rq(env->dst_cpu);
    struct task_struct *cur;
    long src_load, dst_load;
    long load;
    long imp = env->p->numa_group ? groupimp : taskimp;
    long moveimp = imp;
    int dist = env->dist;
    bool assigned = false;

    rcu_read_lock();

    raw_spin_lock_irq(&dst_rq->lock);
    cur = dst_rq->curr;
    /*
     * No need to move the exiting task or idle task.
     */
    if ((cur->flags & PF_EXITING) || is_idle_task(cur))
        cur = NULL;
    else {
        /*
         * The task_struct must be protected here to protect the
         * p->numa_faults access in the task_weight since the
         * numa_faults could already be freed in the following path:
         * finish_task_switch()
         *     --> put_task_struct()
         *     --> __put_task_struct()
         *         --> task_numa_free()
         */
        get_task_struct(cur);
    }

    raw_spin_unlock_irq(&dst_rq->lock);

    /*
     * Because we have preemption enabled we can get migrated around and
     * end try selecting ourselves (current == env->p) as a swap candidate.
     */
    if (cur == env->p)
        goto unlock;

    /*
     * "imp" is the fault differential for the source task between the
     * source and destination node. Calculate the total differential for
     * the source task and potential destination task. The more negative
     * the value is, the more rmeote accesses that would be expected to
     * be incurred if the tasks were swapped.
     */
    if (cur) {
        /* Skip this swap candidate if cannot move to the source cpu */
        if (!cpumask_test_cpu(env->src_cpu, tsk_cpus_allowed(cur)))
            goto unlock;

        /*
         * If dst and source tasks are in the same NUMA group, or not
         * in any group then look only at task weights.
         */
        if (cur->numa_group == env->p->numa_group) {
            imp = taskimp + task_weight(cur, env->src_nid, dist) -
                  task_weight(cur, env->dst_nid, dist);
            /*
             * Add some hysteresis to prevent swapping the
             * tasks within a group over tiny differences.
             */
            if (cur->numa_group)
                imp -= imp/16;
        } else {
            /*
             * Compare the group weights. If a task is all by
             * itself (not part of a group), use the task weight
             * instead.
             */
            if (cur->numa_group)
                imp += group_weight(cur, env->src_nid, dist) -
                       group_weight(cur, env->dst_nid, dist);
            else
                imp += task_weight(cur, env->src_nid, dist) -
                       task_weight(cur, env->dst_nid, dist);
        }
    }

    if (imp <= env->best_imp && moveimp <= env->best_imp)
        goto unlock;

    if (!cur) {
        /* Is there capacity at our destination? */
        if (env->src_stats.nr_running <= env->src_stats.task_capacity &&
            !env->dst_stats.has_free_capacity)
            goto unlock;

        goto balance;
    }

    /* Balance doesn't matter much if we're running a task per cpu */
    if (imp > env->best_imp && src_rq->nr_running == 1 &&
            dst_rq->nr_running == 1)
        goto assign;

    /*
     * In the overloaded case, try and keep the load balanced.
     */
balance:
    load = task_h_load(env->p);
    dst_load = env->dst_stats.load + load;
    src_load = env->src_stats.load - load;

    if (moveimp > imp && moveimp > env->best_imp) {
        /*
         * If the improvement from just moving env->p direction is
         * better than swapping tasks around, check if a move is
         * possible. Store a slightly smaller score than moveimp,
         * so an actually idle CPU will win.
         */
        if (!load_too_imbalanced(src_load, dst_load, env)) {
            imp = moveimp - 1;
            put_task_struct(cur);
            cur = NULL;
            goto assign;
        }
    }

    if (imp <= env->best_imp)
        goto unlock;

    if (cur) {
        load = task_h_load(cur);
        dst_load -= load;
        src_load += load;
    }

    if (load_too_imbalanced(src_load, dst_load, env))
        goto unlock;

    /*
     * One idle CPU per node is evaluated for a task numa move.
     * Call select_idle_sibling to maybe find a better one.
     */
    if (!cur)
        env->dst_cpu = select_idle_sibling(env->p, env->dst_cpu);

assign:
    assigned = true;
    task_numa_assign(env, cur, imp);
unlock:
    rcu_read_unlock();
    /*
     * The dst_rq->curr isn't assigned. The protection for task_struct is
     * finished.
     */
    if (cur && !assigned)
        put_task_struct(cur);
}

static void task_numa_find_cpu(struct task_numa_env *env,
                long taskimp, long groupimp)
{
    int cpu;

    for_each_cpu(cpu, cpumask_of_node(env->dst_nid)) {
        /* Skip this CPU if the source task cannot migrate */
        if (!cpumask_test_cpu(cpu, tsk_cpus_allowed(env->p)))
            continue;

        env->dst_cpu = cpu;
        task_numa_compare(env, taskimp, groupimp);
    }
}

/* Only move tasks to a NUMA node less busy than the current node. */
static bool numa_has_capacity(struct task_numa_env *env)
{
    struct numa_stats *src = &env->src_stats;
    struct numa_stats *dst = &env->dst_stats;

    if (src->has_free_capacity && !dst->has_free_capacity)
        return false;

    /*
     * Only consider a task move if the source has a higher load
     * than the destination, corrected for CPU capacity on each node.
     *
     *      src->load        dst->load
     * --------------------- vs ---------------------
     * src->compute_capacity    dst->compute_capacity
     */
    if (src->load * dst->compute_capacity * env->imbalance_pct >

        dst->load * src->compute_capacity * 100)
        return true;

    return false;
}

static int task_numa_migrate(struct task_struct *p)
{
    struct task_numa_env env = {
        .p = p,

        .src_cpu = task_cpu(p),
        .src_nid = task_node(p),

        .imbalance_pct = 112,

        .best_task = NULL,
        .best_imp = 0,
        .best_cpu = -1,
    };
    struct sched_domain *sd;
    unsigned long taskweight, groupweight;
    int nid, ret, dist;
    long taskimp, groupimp;

    /*
     * Pick the lowest SD_NUMA domain, as that would have the smallest
     * imbalance and would be the first to start moving tasks about.
     *
     * And we want to avoid any moving of tasks about, as that would create
     * random movement of tasks -- counter the numa conditions we're trying
     * to satisfy here.
     */
    rcu_read_lock();
    sd = rcu_dereference(per_cpu(sd_numa, env.src_cpu));
    if (sd)
        env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
    rcu_read_unlock();

    /*
     * Cpusets can break the scheduler domain tree into smaller
     * balance domains, some of which do not cross NUMA boundaries.
     * Tasks that are "trapped" in such domains cannot be migrated
     * elsewhere, so there is no point in (re)trying.
     */
    if (unlikely(!sd)) {
        p->numa_preferred_nid = task_node(p);
        return -EINVAL;
    }

    env.dst_nid = p->numa_preferred_nid;
    dist = env.dist = node_distance(env.src_nid, env.dst_nid);
    taskweight = task_weight(p, env.src_nid, dist);
    groupweight = group_weight(p, env.src_nid, dist);
    update_numa_stats(&env.src_stats, env.src_nid);
    taskimp = task_weight(p, env.dst_nid, dist) - taskweight;
    groupimp = group_weight(p, env.dst_nid, dist) - groupweight;
    update_numa_stats(&env.dst_stats, env.dst_nid);

    /* Try to find a spot on the preferred nid. */
    if (numa_has_capacity(&env))
        task_numa_find_cpu(&env, taskimp, groupimp);

    /*
     * Look at other nodes in these cases:
     * - there is no space available on the preferred_nid
     * - the task is part of a numa_group that is interleaved across
     *   multiple NUMA nodes; in order to better consolidate the group,
     *   we need to check other locations.
     */
    if (env.best_cpu == -1 || (p->numa_group && p->numa_group->active_nodes > 1)) {
        for_each_online_node(nid) {
            if (nid == env.src_nid || nid == p->numa_preferred_nid)
                continue;

            dist = node_distance(env.src_nid, env.dst_nid);
            if (sched_numa_topology_type == NUMA_BACKPLANE &&
                        dist != env.dist) {
                taskweight = task_weight(p, env.src_nid, dist);
                groupweight = group_weight(p, env.src_nid, dist);
            }

            /* Only consider nodes where both task and groups benefit */
            taskimp = task_weight(p, nid, dist) - taskweight;
            groupimp = group_weight(p, nid, dist) - groupweight;
            if (taskimp < 0 && groupimp < 0)
                continue;

            env.dist = dist;
            env.dst_nid = nid;
            update_numa_stats(&env.dst_stats, env.dst_nid);
            if (numa_has_capacity(&env))
                task_numa_find_cpu(&env, taskimp, groupimp);
        }
    }

    /*
     * If the task is part of a workload that spans multiple NUMA nodes,
     * and is migrating into one of the workload's active nodes, remember
     * this node as the task's preferred numa node, so the workload can
     * settle down.
     * A task that migrated to a second choice node will be better off
     * trying for a better one later. Do not set the preferred node here.
     */
    if (p->numa_group) {
        struct numa_group *ng = p->numa_group;

        if (env.best_cpu == -1)
            nid = env.src_nid;
        else
            nid = env.dst_nid;

        if (ng->active_nodes > 1 && numa_is_active_node(env.dst_nid, ng))
            sched_setnuma(p, env.dst_nid);
    }

    /* No better CPU than the current one was found. */
    if (env.best_cpu == -1)
        return -EAGAIN;

    /*
     * Reset the scan period if the task is being rescheduled on an
     * alternative node to recheck if the tasks is now properly placed.
     */
    p->numa_scan_period = task_scan_min(p);

    if (env.best_task == NULL) {
        ret = migrate_task_to(p, env.best_cpu);
        if (ret != 0)
            trace_sched_stick_numa(p, env.src_cpu, env.best_cpu);
        return ret;
    }

    ret = migrate_swap(p, env.best_task);
    if (ret != 0)
        trace_sched_stick_numa(p, env.src_cpu, task_cpu(env.best_task));
    put_task_struct(env.best_task);
    return ret;
}

/* Attempt to migrate a task to a CPU on the preferred node. */
static void numa_migrate_preferred(struct task_struct *p)
{
    unsigned long interval = HZ;

    /* This task has no NUMA fault statistics yet */
    if (unlikely(p->numa_preferred_nid == -1 || !p->numa_faults))
        return;

    /* Periodically retry migrating the task to the preferred node */
    interval = min(interval, msecs_to_jiffies(p->numa_scan_period) / 16);
    p->numa_migrate_retry = jiffies + interval;

    /* Success if task is already running on preferred CPU */
    if (task_node(p) == p->numa_preferred_nid)
        return;

    /* Otherwise, try migrate to a CPU on the preferred node */
    task_numa_migrate(p);
}

/*
 * Find out how many nodes on the workload is actively running on. Do this by
 * tracking the nodes from which NUMA hinting faults are triggered. This can
 * be different from the set of nodes where the workload's memory is currently
 * located.
 */
static void numa_group_count_active_nodes(struct numa_group *numa_group)
{
    unsigned long faults, max_faults = 0;
    int nid, active_nodes = 0;

    for_each_online_node(nid) {
        faults = group_faults_cpu(numa_group, nid);
        if (faults > max_faults)
            max_faults = faults;
    }

    for_each_online_node(nid) {
        faults = group_faults_cpu(numa_group, nid);
        if (faults * ACTIVE_NODE_FRACTION > max_faults)
            active_nodes++;
    }

    numa_group->max_faults_cpu = max_faults;
    numa_group->active_nodes = active_nodes;
}

/*
 * When adapting the scan rate, the period is divided into NUMA_PERIOD_SLOTS
 * increments. The more local the fault statistics are, the higher the scan
 * period will be for the next scan window. If local/(local+remote) ratio is
 * below NUMA_PERIOD_THRESHOLD (where range of ratio is 1..NUMA_PERIOD_SLOTS)
 * the scan period will decrease. Aim for 70% local accesses.
 */
#define NUMA_PERIOD_SLOTS 10
#define NUMA_PERIOD_THRESHOLD 7

/*
 * Increase the scan period (slow down scanning) if the majority of
 * our memory is already on our local node, or if the majority of
 * the page accesses are shared with other processes.
 * Otherwise, decrease the scan period.
 */
static void update_task_scan_period(struct task_struct *p,
            unsigned long shared, unsigned long private)
{
    unsigned int period_slot;
    int ratio;
    int diff;

    unsigned long remote = p->numa_faults_locality[0];
    unsigned long local = p->numa_faults_locality[1];

    /*
     * If there were no record hinting faults then either the task is
     * completely idle or all activity is areas that are not of interest
     * to automatic numa balancing. Related to that, if there were failed
     * migration then it implies we are migrating too quickly or the local
     * node is overloaded. In either case, scan slower
     */
    if (local + shared == 0 || p->numa_faults_locality[2]) {
        p->numa_scan_period = min(p->numa_scan_period_max,
            p->numa_scan_period << 1);

        p->mm->numa_next_scan = jiffies +
            msecs_to_jiffies(p->numa_scan_period);

        return;
    }

    /*
     * Prepare to scale scan period relative to the current period.
     *       == NUMA_PERIOD_THRESHOLD scan period stays the same
     *       <  NUMA_PERIOD_THRESHOLD scan period decreases (scan faster)
     *       >= NUMA_PERIOD_THRESHOLD scan period increases (scan slower)
     */
    period_slot = DIV_ROUND_UP(p->numa_scan_period, NUMA_PERIOD_SLOTS);
    ratio = (local * NUMA_PERIOD_SLOTS) / (local + remote);
    if (ratio >= NUMA_PERIOD_THRESHOLD) {
        int slot = ratio - NUMA_PERIOD_THRESHOLD;
        if (!slot)
            slot = 1;
        diff = slot * period_slot;
    } else {
        diff = -(NUMA_PERIOD_THRESHOLD - ratio) * period_slot;

        /*
         * Scale scan rate increases based on sharing. There is an
         * inverse relationship between the degree of sharing and
         * the adjustment made to the scanning period. Broadly
         * speaking the intent is that there is little point
         * scanning faster if shared accesses dominate as it may
         * simply bounce migrations uselessly
         */
        ratio = DIV_ROUND_UP(private * NUMA_PERIOD_SLOTS, (private + shared + 1));
        diff = (diff * ratio) / NUMA_PERIOD_SLOTS;
    }

    p->numa_scan_period = clamp(p->numa_scan_period + diff,
            task_scan_min(p), task_scan_max(p));
    memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
}

/*
 * Get the fraction of time the task has been running since the last
 * NUMA placement cycle. The scheduler keeps similar statistics, but
 * decays those on a 32ms period, which is orders of magnitude off
 * from the dozens-of-seconds NUMA balancing period. Use the scheduler
 * stats only if the task is so new there are no NUMA statistics yet.
 */
static u64 numa_get_avg_runtime(struct task_struct *p, u64 *period)
{
    u64 runtime, delta, now;
    /* Use the start of this time slice to avoid calculations. */
    now = p->se.exec_start;
    runtime = p->se.sum_exec_runtime;

    if (p->last_task_numa_placement) {
        delta = runtime - p->last_sum_exec_runtime;
        *period = now - p->last_task_numa_placement;
    } else {
        delta = p->se.avg.load_sum / p->se.load.weight;
        *period = LOAD_AVG_MAX;
    }

    p->last_sum_exec_runtime = runtime;
    p->last_task_numa_placement = now;

    return delta;
}

/*
 * Determine the preferred nid for a task in a numa_group. This needs to
 * be done in a way that produces consistent results with group_weight,
 * otherwise workloads might not converge.
 */
static int preferred_group_nid(struct task_struct *p, int nid)
{
    nodemask_t nodes;
    int dist;

    /* Direct connections between all NUMA nodes. */
    if (sched_numa_topology_type == NUMA_DIRECT)
        return nid;

    /*
     * On a system with glueless mesh NUMA topology, group_weight
     * scores nodes according to the number of NUMA hinting faults on
     * both the node itself, and on nearby nodes.
     */
    if (sched_numa_topology_type == NUMA_GLUELESS_MESH) {
        unsigned long score, max_score = 0;
        int node, max_node = nid;

        dist = sched_max_numa_distance;

        for_each_online_node(node) {
            score = group_weight(p, node, dist);
            if (score > max_score) {
                max_score = score;
                max_node = node;
            }
        }
        return max_node;
    }

    /*
     * Finding the preferred nid in a system with NUMA backplane
     * interconnect topology is more involved. The goal is to locate
     * tasks from numa_groups near each other in the system, and
     * untangle workloads from different sides of the system. This requires
     * searching down the hierarchy of node groups, recursively searching
     * inside the highest scoring group of nodes. The nodemask tricks
     * keep the complexity of the search down.
     */
    nodes = node_online_map;
    for (dist = sched_max_numa_distance; dist > LOCAL_DISTANCE; dist--) {
        unsigned long max_faults = 0;
        nodemask_t max_group = NODE_MASK_NONE;
        int a, b;

        /* Are there nodes at this distance from each other? */
        if (!find_numa_distance(dist))
            continue;

        for_each_node_mask(a, nodes) {
            unsigned long faults = 0;
            nodemask_t this_group;
            nodes_clear(this_group);

            /* Sum group's NUMA faults; includes a==b case. */
            for_each_node_mask(b, nodes) {
                if (node_distance(a, b) < dist) {
                    faults += group_faults(p, b);
                    node_set(b, this_group);
                    node_clear(b, nodes);
                }
            }

            /* Remember the top group. */
            if (faults > max_faults) {
                max_faults = faults;
                max_group = this_group;
                /*
                 * subtle: at the smallest distance there is
                 * just one node left in each "group", the
                 * winner is the preferred nid.
                 */
                nid = a;
            }
        }
        /* Next round, evaluate the nodes within max_group. */
        if (!max_faults)
            break;
        nodes = max_group;
    }
    return nid;
}

static void task_numa_placement(struct task_struct *p)
{
    int seq, nid, max_nid = -1, max_group_nid = -1;
    unsigned long max_faults = 0, max_group_faults = 0;
    unsigned long fault_types[2] = { 0, 0 };
    unsigned long total_faults;
    u64 runtime, period;
    spinlock_t *group_lock = NULL;

    /*
     * The p->mm->numa_scan_seq field gets updated without
     * exclusive access. Use READ_ONCE() here to ensure
     * that the field is read in a single access:
     */
    seq = READ_ONCE(p->mm->numa_scan_seq);
    if (p->numa_scan_seq == seq)
        return;
    p->numa_scan_seq = seq;
    p->numa_scan_period_max = task_scan_max(p);

    total_faults = p->numa_faults_locality[0] +
               p->numa_faults_locality[1];
    runtime = numa_get_avg_runtime(p, &period);

    /* If the task is part of a group prevent parallel updates to group stats */
    if (p->numa_group) {
        group_lock = &p->numa_group->lock;
        spin_lock_irq(group_lock);
    }

    /* Find the node with the highest number of faults */
    for_each_online_node(nid) {
        /* Keep track of the offsets in numa_faults array */
        int mem_idx, membuf_idx, cpu_idx, cpubuf_idx;
        unsigned long faults = 0, group_faults = 0;
        int priv;

        for (priv = 0; priv < NR_NUMA_HINT_FAULT_TYPES; priv++) {
            long diff, f_diff, f_weight;

            mem_idx = task_faults_idx(NUMA_MEM, nid, priv);
            membuf_idx = task_faults_idx(NUMA_MEMBUF, nid, priv);
            cpu_idx = task_faults_idx(NUMA_CPU, nid, priv);
            cpubuf_idx = task_faults_idx(NUMA_CPUBUF, nid, priv);

            /* Decay existing window, copy faults since last scan */
            diff = p->numa_faults[membuf_idx] - p->numa_faults[mem_idx] / 2;
            fault_types[priv] += p->numa_faults[membuf_idx];
            p->numa_faults[membuf_idx] = 0;

            /*
             * Normalize the faults_from, so all tasks in a group
             * count according to CPU use, instead of by the raw
             * number of faults. Tasks with little runtime have
             * little over-all impact on throughput, and thus their
             * faults are less important.
             */
            f_weight = div64_u64(runtime << 16, period + 1);
            f_weight = (f_weight * p->numa_faults[cpubuf_idx]) /
                   (total_faults + 1);
            f_diff = f_weight - p->numa_faults[cpu_idx] / 2;
            p->numa_faults[cpubuf_idx] = 0;

            p->numa_faults[mem_idx] += diff;
            p->numa_faults[cpu_idx] += f_diff;
            faults += p->numa_faults[mem_idx];
            p->total_numa_faults += diff;
            if (p->numa_group) {
                /*
                 * safe because we can only change our own group
                 *
                 * mem_idx represents the offset for a given
                 * nid and priv in a specific region because it
                 * is at the beginning of the numa_faults array.
                 */
                p->numa_group->faults[mem_idx] += diff;
                p->numa_group->faults_cpu[mem_idx] += f_diff;
                p->numa_group->total_faults += diff;
                group_faults += p->numa_group->faults[mem_idx];
            }
        }

        if (faults > max_faults) {
            max_faults = faults;
            max_nid = nid;
        }

        if (group_faults > max_group_faults) {
            max_group_faults = group_faults;
            max_group_nid = nid;
        }
    }

    update_task_scan_period(p, fault_types[0], fault_types[1]);

    if (p->numa_group) {
        numa_group_count_active_nodes(p->numa_group);
        spin_unlock_irq(group_lock);
        max_nid = preferred_group_nid(p, max_group_nid);
    }

    if (max_faults) {
        /* Set the new preferred node */
        if (max_nid != p->numa_preferred_nid)
            sched_setnuma(p, max_nid);

        if (task_node(p) != p->numa_preferred_nid)
            numa_migrate_preferred(p);
    }
}

static inline int get_numa_group(struct numa_group *grp)
{
    return atomic_inc_not_zero(&grp->refcount);
}

static inline void put_numa_group(struct numa_group *grp)
{
    if (atomic_dec_and_test(&grp->refcount))
        kfree_rcu(grp, rcu);
}

static void task_numa_group(struct task_struct *p, int cpupid, int flags,
            int *priv)
{
    struct numa_group *grp, *my_grp;
    struct task_struct *tsk;
    bool join = false;
    int cpu = cpupid_to_cpu(cpupid);
    int i;

    if (unlikely(!p->numa_group)) {
        unsigned int size = sizeof(struct numa_group) +
                    4*nr_node_ids*sizeof(unsigned long);

        grp = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
        if (!grp)
            return;

        atomic_set(&grp->refcount, 1);
        grp->active_nodes = 1;
        grp->max_faults_cpu = 0;
        spin_lock_init(&grp->lock);
        grp->gid = p->pid;
        /* Second half of the array tracks nids where faults happen */
        grp->faults_cpu = grp->faults + NR_NUMA_HINT_FAULT_TYPES *
                        nr_node_ids;

        for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
            grp->faults[i] = p->numa_faults[i];

        grp->total_faults = p->total_numa_faults;

        grp->nr_tasks++;
        rcu_assign_pointer(p->numa_group, grp);
    }

    rcu_read_lock();
    tsk = READ_ONCE(cpu_rq(cpu)->curr);

    if (!cpupid_match_pid(tsk, cpupid))
        goto no_join;

    grp = rcu_dereference(tsk->numa_group);
    if (!grp)
        goto no_join;

    my_grp = p->numa_group;
    if (grp == my_grp)
        goto no_join;

    /*
     * Only join the other group if its bigger; if we're the bigger group,
     * the other task will join us.
     */
    if (my_grp->nr_tasks > grp->nr_tasks)
        goto no_join;

    /*
     * Tie-break on the grp address.
     */
    if (my_grp->nr_tasks == grp->nr_tasks && my_grp > grp)
        goto no_join;

    /* Always join threads in the same process. */
    if (tsk->mm == current->mm)
        join = true;

    /* Simple filter to avoid false positives due to PID collisions */
    if (flags & TNF_SHARED)
        join = true;

    /* Update priv based on whether false sharing was detected */
    *priv = !join;

    if (join && !get_numa_group(grp))
        goto no_join;

    rcu_read_unlock();

    if (!join)
        return;

    BUG_ON(irqs_disabled());
    double_lock_irq(&my_grp->lock, &grp->lock);

    for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++) {
        my_grp->faults[i] -= p->numa_faults[i];
        grp->faults[i] += p->numa_faults[i];
    }
    my_grp->total_faults -= p->total_numa_faults;
    grp->total_faults += p->total_numa_faults;

    my_grp->nr_tasks--;
    grp->nr_tasks++;

    spin_unlock(&my_grp->lock);
    spin_unlock_irq(&grp->lock);

    rcu_assign_pointer(p->numa_group, grp);

    put_numa_group(my_grp);
    return;

no_join:
    rcu_read_unlock();
    return;
}

void task_numa_free(struct task_struct *p)
{
    struct numa_group *grp = p->numa_group;
    void *numa_faults = p->numa_faults;
    unsigned long flags;
    int i;

    if (grp) {
        spin_lock_irqsave(&grp->lock, flags);
        for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
            grp->faults[i] -= p->numa_faults[i];
        grp->total_faults -= p->total_numa_faults;

        grp->nr_tasks--;
        spin_unlock_irqrestore(&grp->lock, flags);
        RCU_INIT_POINTER(p->numa_group, NULL);
        put_numa_group(grp);
    }

    p->numa_faults = NULL;
    kfree(numa_faults);
}

/*
 * Got a PROT_NONE fault for a page on @node.
 */
void task_numa_fault(int last_cpupid, int mem_node, int pages, int flags)
{
    struct task_struct *p = current;
    bool migrated = flags & TNF_MIGRATED;
    int cpu_node = task_node(current);
    int local = !!(flags & TNF_FAULT_LOCAL);
    struct numa_group *ng;
    int priv;

    if (!static_branch_likely(&sched_numa_balancing))
        return;

    /* for example, ksmd faulting in a user's mm */
    if (!p->mm)
        return;

    /* Allocate buffer to track faults on a per-node basis */
    if (unlikely(!p->numa_faults)) {
        int size = sizeof(*p->numa_faults) *
               NR_NUMA_HINT_FAULT_BUCKETS * nr_node_ids;

        p->numa_faults = kzalloc(size, GFP_KERNEL|__GFP_NOWARN);
        if (!p->numa_faults)
            return;

        p->total_numa_faults = 0;
        memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
    }

    /*
     * First accesses are treated as private, otherwise consider accesses
     * to be private if the accessing pid has not changed
     */
    if (unlikely(last_cpupid == (-1 & LAST_CPUPID_MASK))) {
        priv = 1;
    } else {
        priv = cpupid_match_pid(p, last_cpupid);
        if (!priv && !(flags & TNF_NO_GROUP))
            task_numa_group(p, last_cpupid, flags, &priv);
    }

    /*
     * If a workload spans multiple NUMA nodes, a shared fault that
     * occurs wholly within the set of nodes that the workload is
     * actively using should be counted as local. This allows the
     * scan rate to slow down when a workload has settled down.
     */
    ng = p->numa_group;
    if (!priv && !local && ng && ng->active_nodes > 1 &&
                numa_is_active_node(cpu_node, ng) &&
                numa_is_active_node(mem_node, ng))
        local = 1;

    task_numa_placement(p);

    /*
     * Retry task to preferred node migration periodically, in case it
     * case it previously failed, or the scheduler moved us.
     */
    if (time_after(jiffies, p->numa_migrate_retry))
        numa_migrate_preferred(p);

    if (migrated)
        p->numa_pages_migrated += pages;
    if (flags & TNF_MIGRATE_FAIL)
        p->numa_faults_locality[2] += pages;

    p->numa_faults[task_faults_idx(NUMA_MEMBUF, mem_node, priv)] += pages;
    p->numa_faults[task_faults_idx(NUMA_CPUBUF, cpu_node, priv)] += pages;
    p->numa_faults_locality[local] += pages;
}

static void reset_ptenuma_scan(struct task_struct *p)
{
    /*
     * We only did a read acquisition of the mmap sem, so
     * p->mm->numa_scan_seq is written to without exclusive access
     * and the update is not guaranteed to be atomic. That's not
     * much of an issue though, since this is just used for
     * statistical sampling. Use READ_ONCE/WRITE_ONCE, which are not
     * expensive, to avoid any form of compiler optimizations:
     */
    WRITE_ONCE(p->mm->numa_scan_seq, READ_ONCE(p->mm->numa_scan_seq) + 1);
    p->mm->numa_scan_offset = 0;
}

/*
 * The expensive part of numa migration is done from task_work context.
 * Triggered from task_tick_numa().
 */
void task_numa_work(struct callback_head *work)
{
    unsigned long migrate, next_scan, now = jiffies;
    struct task_struct *p = current;
    struct mm_struct *mm = p->mm;
    u64 runtime = p->se.sum_exec_runtime;
    struct vm_area_struct *vma;
    unsigned long start, end;
    unsigned long nr_pte_updates = 0;
    long pages, virtpages;

    WARN_ON_ONCE(p != container_of(work, struct task_struct, numa_work));

    work->next = work; /* protect against double add */
    /*
     * Who cares about NUMA placement when they're dying.
     *
     * NOTE: make sure not to dereference p->mm before this check,
     * exit_task_work() happens _after_ exit_mm() so we could be called
     * without p->mm even though we still had it when we enqueued this
     * work.
     */
    if (p->flags & PF_EXITING)
        return;

    if (!mm->numa_next_scan) {
        mm->numa_next_scan = now +
            msecs_to_jiffies(sysctl_numa_balancing_scan_delay);
    }

    /*
     * Enforce maximal scan/migration frequency..
     */
    migrate = mm->numa_next_scan;
    if (time_before(now, migrate))
        return;

    if (p->numa_scan_period == 0) {
        p->numa_scan_period_max = task_scan_max(p);
        p->numa_scan_period = task_scan_min(p);
    }

    next_scan = now + msecs_to_jiffies(p->numa_scan_period);
    if (cmpxchg(&mm->numa_next_scan, migrate, next_scan) != migrate)
        return;

    /*
     * Delay this task enough that another task of this mm will likely win
     * the next time around.
     */
    p->node_stamp += 2 * TICK_NSEC;

    start = mm->numa_scan_offset;
    pages = sysctl_numa_balancing_scan_size;
    pages <<= 20 - PAGE_SHIFT; /* MB in pages */
    virtpages = pages * 8;     /* Scan up to this much virtual space */
    if (!pages)
        return;


    down_read(&mm->mmap_sem);
    vma = find_vma(mm, start);
    if (!vma) {
        reset_ptenuma_scan(p);
        start = 0;
        vma = mm->mmap;
    }
    for (; vma; vma = vma->vm_next) {
        if (!vma_migratable(vma) || !vma_policy_mof(vma) ||
            is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_MIXEDMAP)) {
            continue;
        }

        /*
         * Shared library pages mapped by multiple processes are not
         * migrated as it is expected they are cache replicated. Avoid
         * hinting faults in read-only file-backed mappings or the vdso
         * as migrating the pages will be of marginal benefit.
         */
        if (!vma->vm_mm ||
            (vma->vm_file && (vma->vm_flags & (VM_READ|VM_WRITE)) == (VM_READ)))
            continue;

        /*
         * Skip inaccessible VMAs to avoid any confusion between
         * PROT_NONE and NUMA hinting ptes
         */
        if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
            continue;

        do {
            start = max(start, vma->vm_start);
            end = ALIGN(start + (pages << PAGE_SHIFT), HPAGE_SIZE);
            end = min(end, vma->vm_end);
            nr_pte_updates = change_prot_numa(vma, start, end);

            /*
             * Try to scan sysctl_numa_balancing_size worth of
             * hpages that have at least one present PTE that
             * is not already pte-numa. If the VMA contains
             * areas that are unused or already full of prot_numa
             * PTEs, scan up to virtpages, to skip through those
             * areas faster.
             */
            if (nr_pte_updates)
                pages -= (end - start) >> PAGE_SHIFT;
            virtpages -= (end - start) >> PAGE_SHIFT;

            start = end;
            if (pages <= 0 || virtpages <= 0)
                goto out;

            cond_resched();
        } while (end != vma->vm_end);
    }

out:
    /*
     * It is possible to reach the end of the VMA list but the last few
     * VMAs are not guaranteed to the vma_migratable. If they are not, we
     * would find the !migratable VMA on the next scan but not reset the
     * scanner to the start so check it now.
     */
    if (vma)
        mm->numa_scan_offset = start;
    else
        reset_ptenuma_scan(p);
    up_read(&mm->mmap_sem);

    /*
     * Make sure tasks use at least 32x as much time to run other code
     * than they used here, to limit NUMA PTE scanning overhead to 3% max.
     * Usually update_task_scan_period slows down scanning enough; on an
     * overloaded system we need to limit overhead on a per task basis.
     */
    if (unlikely(p->se.sum_exec_runtime != runtime)) {
        u64 diff = p->se.sum_exec_runtime - runtime;
        p->node_stamp += 32 * diff;
    }
}

/*
 * Drive the periodic memory faults..
 */
void task_tick_numa(struct rq *rq, struct task_struct *curr)
{
    struct callback_head *work = &curr->numa_work;
    u64 period, now;

    /*
     * We don't care about NUMA placement if we don't have memory.
     */
    if (!curr->mm || (curr->flags & PF_EXITING) || work->next != work)
        return;

    /*
     * Using runtime rather than walltime has the dual advantage that
     * we (mostly) drive the selection from busy threads and that the
     * task needs to have done some actual work before we bother with
     * NUMA placement.
     */
    now = curr->se.sum_exec_runtime;
    period = (u64)curr->numa_scan_period * NSEC_PER_MSEC;

    if (now > curr->node_stamp + period) {
        if (!curr->node_stamp)
            curr->numa_scan_period = task_scan_min(curr);
        curr->node_stamp += period;

        if (!time_before(jiffies, curr->mm->numa_next_scan)) {
            init_task_work(work, task_numa_work); /* TODO: move this into sched_fork() */
            task_work_add(curr, work, true);
        }
    }
}
#else
static void task_tick_numa(struct rq *rq, struct task_struct *curr)
{
}

static inline void account_numa_enqueue(struct rq *rq, struct task_struct *p)
{
}

static inline void account_numa_dequeue(struct rq *rq, struct task_struct *p)
{
}
#endif /* CONFIG_NUMA_BALANCING */

static void
account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    update_load_add(&cfs_rq->load, se->load.weight);
    if (!parent_entity(se))
        update_load_add(&rq_of(cfs_rq)->load, se->load.weight);
#ifdef CONFIG_SMP
    if (entity_is_task(se)) {
        struct rq *rq = rq_of(cfs_rq);

        account_numa_enqueue(rq, task_of(se));
        list_add(&se->group_node, &rq->cfs_tasks);
    }
#endif
    cfs_rq->nr_running++;
}

static void
account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    update_load_sub(&cfs_rq->load, se->load.weight);
    if (!parent_entity(se))
        update_load_sub(&rq_of(cfs_rq)->load, se->load.weight);
    if (entity_is_task(se)) {
        account_numa_dequeue(rq_of(cfs_rq), task_of(se));
        list_del_init(&se->group_node);
    }
    cfs_rq->nr_running--;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
# ifdef CONFIG_SMP
static inline long calc_tg_weight(struct task_group *tg, struct cfs_rq *cfs_rq)
{
    long tg_weight;

    /*
     * Use this CPU's real-time load instead of the last load contribution
     * as the updating of the contribution is delayed, and we will use the
     * the real-time load to calc the share. See update_tg_load_avg().
     */
    tg_weight = atomic_long_read(&tg->load_avg);
    tg_weight -= cfs_rq->tg_load_avg_contrib;
    tg_weight += cfs_rq->load.weight;

    return tg_weight;
}

static long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
{
    long tg_weight, load, shares;

    tg_weight = calc_tg_weight(tg, cfs_rq);
    load = cfs_rq->load.weight;

    shares = (tg->shares * load);
    if (tg_weight)
        shares /= tg_weight;

    if (shares < MIN_SHARES)
        shares = MIN_SHARES;
    if (shares > tg->shares)
        shares = tg->shares;

    return shares;
}
# else /* CONFIG_SMP */
static inline long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
{
    return tg->shares;
}
# endif /* CONFIG_SMP */
static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
                unsigned long weight)
{
    if (se->on_rq) {
        /* commit outstanding execution time */
        if (cfs_rq->curr == se)
            update_curr(cfs_rq);
        account_entity_dequeue(cfs_rq, se);
    }

    update_load_set(&se->load, weight);

    if (se->on_rq)
        account_entity_enqueue(cfs_rq, se);
}

static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);

static void update_cfs_shares(struct cfs_rq *cfs_rq)
{
    struct task_group *tg;
    struct sched_entity *se;
    long shares;

    tg = cfs_rq->tg;
    se = tg->se[cpu_of(rq_of(cfs_rq))];
    if (!se || throttled_hierarchy(cfs_rq))
        return;
#ifndef CONFIG_SMP
    if (likely(se->load.weight == tg->shares))
        return;
#endif
    shares = calc_cfs_shares(cfs_rq, tg);

    reweight_entity(cfs_rq_of(se), se, shares);
}
#else /* CONFIG_FAIR_GROUP_SCHED */
static inline void update_cfs_shares(struct cfs_rq *cfs_rq)
{
}
#endif /* CONFIG_FAIR_GROUP_SCHED */

#ifdef CONFIG_SMP
/* Precomputed fixed inverse multiplies for multiplication by y^n */
static const u32 runnable_avg_yN_inv[] = {
    0xffffffff, 0xfa83b2da, 0xf5257d14, 0xefe4b99a, 0xeac0c6e6, 0xe5b906e6,
    0xe0ccdeeb, 0xdbfbb796, 0xd744fcc9, 0xd2a81d91, 0xce248c14, 0xc9b9bd85,
    0xc5672a10, 0xc12c4cc9, 0xbd08a39e, 0xb8fbaf46, 0xb504f333, 0xb123f581,
    0xad583ee9, 0xa9a15ab4, 0xa5fed6a9, 0xa2704302, 0x9ef5325f, 0x9b8d39b9,
    0x9837f050, 0x94f4efa8, 0x91c3d373, 0x8ea4398a, 0x8b95c1e3, 0x88980e80,
    0x85aac367, 0x82cd8698,
};

/*
 * Precomputed \Sum y^k { 1<=k<=n }.  These are floor(true_value) to prevent
 * over-estimates when re-combining.
 */
static const u32 runnable_avg_yN_sum[] = {
        0, 1002, 1982, 2941, 3880, 4798, 5697, 6576, 7437, 8279, 9103,
     9909,10698,11470,12226,12966,13690,14398,15091,15769,16433,17082,
    17718,18340,18949,19545,20128,20698,21256,21802,22336,22859,23371,
};

/*
 * Approximate:
 *   val * y^n,    where y^32 ~= 0.5 (~1 scheduling period)
 */
static __always_inline u64 decay_load(u64 val, u64 n)
{
    unsigned int local_n;

    if (!n)
        return val;
    else if (unlikely(n > LOAD_AVG_PERIOD * 63))
        return 0;

    /* after bounds checking we can collapse to 32-bit */
    local_n = n;

    /*
     * As y^PERIOD = 1/2, we can combine
     *    y^n = 1/2^(n/PERIOD) * y^(n%PERIOD)
     * With a look-up table which covers y^n (n<PERIOD)
     *
     * To achieve constant time decay_load.
     */
    if (unlikely(local_n >= LOAD_AVG_PERIOD)) {
        val >>= local_n / LOAD_AVG_PERIOD;
        local_n %= LOAD_AVG_PERIOD;
    }

    val = mul_u64_u32_shr(val, runnable_avg_yN_inv[local_n], 32);
    return val;
}

/*
 * For updates fully spanning n periods, the contribution to runnable
 * average will be: \Sum 1024*y^n
 *
 * We can compute this reasonably efficiently by combining:
 *   y^PERIOD = 1/2 with precomputed \Sum 1024*y^n {for  n <PERIOD}
 */
static u32 __compute_runnable_contrib(u64 n)
{
    u32 contrib = 0;

    if (likely(n <= LOAD_AVG_PERIOD))
        return runnable_avg_yN_sum[n];
    else if (unlikely(n >= LOAD_AVG_MAX_N))
        return LOAD_AVG_MAX;

    /* Compute \Sum k^n combining precomputed values for k^i, \Sum k^j */
    do {
        contrib /= 2; /* y^LOAD_AVG_PERIOD = 1/2 */
        contrib += runnable_avg_yN_sum[LOAD_AVG_PERIOD];

        n -= LOAD_AVG_PERIOD;
    } while (n > LOAD_AVG_PERIOD);

    contrib = decay_load(contrib, n);
    return contrib + runnable_avg_yN_sum[n];
}

#if (SCHED_LOAD_SHIFT - SCHED_LOAD_RESOLUTION) != 10 || SCHED_CAPACITY_SHIFT != 10
#error "load tracking assumes 2^10 as unit"
#endif

#define cap_scale(v, s) ((v)*(s) >> SCHED_CAPACITY_SHIFT)

/*
 * We can represent the historical contribution to runnable average as the
 * coefficients of a geometric series.  To do this we sub-divide our runnable
 * history into segments of approximately 1ms (1024us); label the segment that
 * occurred N-ms ago p_N, with p_0 corresponding to the current period, e.g.
 *
 * [<- 1024us ->|<- 1024us ->|<- 1024us ->| ...
 *      p0        p1       p2
 *     (now)       (~1ms ago)  (~2ms ago)
 *
 * Let u_i denote the fraction of p_i that the entity was runnable.
 *
 * We then designate the fractions u_i as our co-efficients, yielding the
 * following representation of historical load:
 *   u_0 + u_1*y + u_2*y^2 + u_3*y^3 + ...
 *
 * We choose y based on the with of a reasonably scheduling period, fixing:
 *   y^32 = 0.5
 *
 * This means that the contribution to load ~32ms ago (u_32) will be weighted
 * approximately half as much as the contribution to load within the last ms
 * (u_0).
 *
 * When a period "rolls over" and we have new u_0`, multiplying the previous
 * sum again by y is sufficient to update:
 *   load_avg = u_0` + y*(u_0 + u_1*y + u_2*y^2 + ... )
 *        = u_0 + u_1*y + u_2*y^2 + ... [re-labeling u_i --> u_{i+1}]
 */
static __always_inline int
__update_load_avg(u64 now, int cpu, struct sched_avg *sa,
          unsigned long weight, int running, struct cfs_rq *cfs_rq)
{
    u64 delta, scaled_delta, periods;
    u32 contrib;
    unsigned int delta_w, scaled_delta_w, decayed = 0;
    unsigned long scale_freq, scale_cpu;

    delta = now - sa->last_update_time;
    /*
     * This should only happen when time goes backwards, which it
     * unfortunately does during sched clock init when we swap over to TSC.
     */
    if ((s64)delta < 0) {
        sa->last_update_time = now;
        return 0;
    }

    /*
     * Use 1024ns as the unit of measurement since it's a reasonable
     * approximation of 1us and fast to compute.
     */
    delta >>= 10;
    if (!delta)
        return 0;
    sa->last_update_time = now;

    scale_freq = arch_scale_freq_capacity(NULL, cpu);
    scale_cpu = arch_scale_cpu_capacity(NULL, cpu);

    /* delta_w is the amount already accumulated against our next period */
    delta_w = sa->period_contrib;
    if (delta + delta_w >= 1024) {
        decayed = 1;

        /* how much left for next period will start over, we don't know yet */
        sa->period_contrib = 0;

        /*
         * Now that we know we're crossing a period boundary, figure
         * out how much from delta we need to complete the current
         * period and accrue it.
         */
        delta_w = 1024 - delta_w;
        scaled_delta_w = cap_scale(delta_w, scale_freq);
        if (weight) {
            sa->load_sum += weight * scaled_delta_w;
            if (cfs_rq) {
                cfs_rq->runnable_load_sum +=
                        weight * scaled_delta_w;
            }
        }
        if (running)
            sa->util_sum += scaled_delta_w * scale_cpu;

        delta -= delta_w;

        /* Figure out how many additional periods this update spans */
        periods = delta / 1024;
        delta %= 1024;

        sa->load_sum = decay_load(sa->load_sum, periods + 1);
        if (cfs_rq) {
            cfs_rq->runnable_load_sum =
                decay_load(cfs_rq->runnable_load_sum, periods + 1);
        }
        sa->util_sum = decay_load((u64)(sa->util_sum), periods + 1);

        /* Efficiently calculate \sum (1..n_period) 1024*y^i */
        contrib = __compute_runnable_contrib(periods);
        contrib = cap_scale(contrib, scale_freq);
        if (weight) {
            sa->load_sum += weight * contrib;
            if (cfs_rq)
                cfs_rq->runnable_load_sum += weight * contrib;
        }
        if (running)
            sa->util_sum += contrib * scale_cpu;
    }

    /* Remainder of delta accrued against u_0` */
    scaled_delta = cap_scale(delta, scale_freq);
    if (weight) {
        sa->load_sum += weight * scaled_delta;
        if (cfs_rq)
            cfs_rq->runnable_load_sum += weight * scaled_delta;
    }
    if (running)
        sa->util_sum += scaled_delta * scale_cpu;

    sa->period_contrib += delta;

    if (decayed) {
        sa->load_avg = div_u64(sa->load_sum, LOAD_AVG_MAX);
        if (cfs_rq) {
            cfs_rq->runnable_load_avg =
                div_u64(cfs_rq->runnable_load_sum, LOAD_AVG_MAX);
        }
        sa->util_avg = sa->util_sum / LOAD_AVG_MAX;
    }

    return decayed;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
/*
 * Updating tg's load_avg is necessary before update_cfs_share (which is done)
 * and effective_load (which is not done because it is too costly).
 */
static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
{
    long delta = cfs_rq->avg.load_avg - cfs_rq->tg_load_avg_contrib;

    /*
     * No need to update load_avg for root_task_group as it is not used.
     */
    if (cfs_rq->tg == &root_task_group)
        return;

    if (force || abs(delta) > cfs_rq->tg_load_avg_contrib / 64) {
        atomic_long_add(delta, &cfs_rq->tg->load_avg);
        cfs_rq->tg_load_avg_contrib = cfs_rq->avg.load_avg;
    }
}

/*
 * Called within set_task_rq() right before setting a task's cpu. The
 * caller only guarantees p->pi_lock is held; no other assumptions,
 * including the state of rq->lock, should be made.
 */
void set_task_rq_fair(struct sched_entity *se,
              struct cfs_rq *prev, struct cfs_rq *next)
{
    if (!sched_feat(ATTACH_AGE_LOAD))
        return;

    /*
     * We are supposed to update the task to "current" time, then its up to
     * date and ready to go to new CPU/cfs_rq. But we have difficulty in
     * getting what current time is, so simply throw away the out-of-date
     * time. This will result in the wakee task is less decayed, but giving
     * the wakee more load sounds not bad.
     */
    if (se->avg.last_update_time && prev) {
        u64 p_last_update_time;
        u64 n_last_update_time;

#ifndef CONFIG_64BIT
        u64 p_last_update_time_copy;
        u64 n_last_update_time_copy;

        do {
            p_last_update_time_copy = prev->load_last_update_time_copy;
            n_last_update_time_copy = next->load_last_update_time_copy;

            smp_rmb();

            p_last_update_time = prev->avg.last_update_time;
            n_last_update_time = next->avg.last_update_time;

        } while (p_last_update_time != p_last_update_time_copy ||
             n_last_update_time != n_last_update_time_copy);
#else
        p_last_update_time = prev->avg.last_update_time;
        n_last_update_time = next->avg.last_update_time;
#endif
        __update_load_avg(p_last_update_time, cpu_of(rq_of(prev)),
                  &se->avg, 0, 0, NULL);
        se->avg.last_update_time = n_last_update_time;
    }
}
#else /* CONFIG_FAIR_GROUP_SCHED */
static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force) {}
#endif /* CONFIG_FAIR_GROUP_SCHED */

static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq);

/* Group cfs_rq's load_avg is used for task_h_load and update_cfs_share */
static inline int update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
{
    struct sched_avg *sa = &cfs_rq->avg;
    int decayed, removed = 0;

    if (atomic_long_read(&cfs_rq->removed_load_avg)) {
        s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);
        sa->load_avg = max_t(long, sa->load_avg - r, 0);
        sa->load_sum = max_t(s64, sa->load_sum - r * LOAD_AVG_MAX, 0);
        removed = 1;
    }

    if (atomic_long_read(&cfs_rq->removed_util_avg)) {
        long r = atomic_long_xchg(&cfs_rq->removed_util_avg, 0);
        sa->util_avg = max_t(long, sa->util_avg - r, 0);
        sa->util_sum = max_t(s32, sa->util_sum - r * LOAD_AVG_MAX, 0);
    }

    decayed = __update_load_avg(now, cpu_of(rq_of(cfs_rq)), sa,
        scale_load_down(cfs_rq->load.weight), cfs_rq->curr != NULL, cfs_rq);

#ifndef CONFIG_64BIT
    smp_wmb();
    cfs_rq->load_last_update_time_copy = sa->last_update_time;
#endif

    return decayed || removed;
}

/* Update task and its cfs_rq load average */
static inline void update_load_avg(struct sched_entity *se, int update_tg)
{
    struct cfs_rq *cfs_rq = cfs_rq_of(se);
    u64 now = cfs_rq_clock_task(cfs_rq);
    struct rq *rq = rq_of(cfs_rq);
    int cpu = cpu_of(rq);

    /*
     * Track task load average for carrying it to new CPU after migrated, and
     * track group sched_entity load average for task_h_load calc in migration
     */
    __update_load_avg(now, cpu, &se->avg,
              se->on_rq * scale_load_down(se->load.weight),
              cfs_rq->curr == se, NULL);

    if (update_cfs_rq_load_avg(now, cfs_rq) && update_tg)
        update_tg_load_avg(cfs_rq, 0);

    if (cpu == smp_processor_id() && &rq->cfs == cfs_rq) {
        unsigned long max = rq->cpu_capacity_orig;

        /*
         * There are a few boundary cases this might miss but it should
         * get called often enough that that should (hopefully) not be
         * a real problem -- added to that it only calls on the local
         * CPU, so if we enqueue remotely we'll miss an update, but
         * the next tick/schedule should update.
         *
         * It will not get called when we go idle, because the idle
         * thread is a different class (!fair), nor will the utilization
         * number include things like RT tasks.
         *
         * As is, the util number is not freq-invariant (we'd have to
         * implement arch_scale_freq_capacity() for that).
         *
         * See cpu_util().
         */
        cpufreq_update_util(rq_clock(rq),
                    min(cfs_rq->avg.util_avg, max), max);
    }
}

static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    if (!sched_feat(ATTACH_AGE_LOAD))
        goto skip_aging;

    /*
     * If we got migrated (either between CPUs or between cgroups) we'll
     * have aged the average right before clearing @last_update_time.
     */
    if (se->avg.last_update_time) {
        __update_load_avg(cfs_rq->avg.last_update_time, cpu_of(rq_of(cfs_rq)),
                  &se->avg, 0, 0, NULL);

        /*
         * XXX: we could have just aged the entire load away if we've been
         * absent from the fair class for too long.
         */
    }

skip_aging:
    se->avg.last_update_time = cfs_rq->avg.last_update_time;
    cfs_rq->avg.load_avg += se->avg.load_avg;
    cfs_rq->avg.load_sum += se->avg.load_sum;
    cfs_rq->avg.util_avg += se->avg.util_avg;
    cfs_rq->avg.util_sum += se->avg.util_sum;
}

static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    __update_load_avg(cfs_rq->avg.last_update_time, cpu_of(rq_of(cfs_rq)),
              &se->avg, se->on_rq * scale_load_down(se->load.weight),
              cfs_rq->curr == se, NULL);

    cfs_rq->avg.load_avg = max_t(long, cfs_rq->avg.load_avg - se->avg.load_avg, 0);
    cfs_rq->avg.load_sum = max_t(s64,  cfs_rq->avg.load_sum - se->avg.load_sum, 0);
    cfs_rq->avg.util_avg = max_t(long, cfs_rq->avg.util_avg - se->avg.util_avg, 0);
    cfs_rq->avg.util_sum = max_t(s32,  cfs_rq->avg.util_sum - se->avg.util_sum, 0);
}

/* Add the load generated by se into cfs_rq's load average */
static inline void
enqueue_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    struct sched_avg *sa = &se->avg;
    u64 now = cfs_rq_clock_task(cfs_rq);
    int migrated, decayed;

    migrated = !sa->last_update_time;
    if (!migrated) {
        __update_load_avg(now, cpu_of(rq_of(cfs_rq)), sa,
            se->on_rq * scale_load_down(se->load.weight),
            cfs_rq->curr == se, NULL);
    }

    decayed = update_cfs_rq_load_avg(now, cfs_rq);

    cfs_rq->runnable_load_avg += sa->load_avg;
    cfs_rq->runnable_load_sum += sa->load_sum;

    if (migrated)
        attach_entity_load_avg(cfs_rq, se);

    if (decayed || migrated)
        update_tg_load_avg(cfs_rq, 0);
}

/* Remove the runnable load generated by se from cfs_rq's runnable load average */
static inline void
dequeue_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    update_load_avg(se, 1);

    cfs_rq->runnable_load_avg =
        max_t(long, cfs_rq->runnable_load_avg - se->avg.load_avg, 0);
    cfs_rq->runnable_load_sum =
        max_t(s64,  cfs_rq->runnable_load_sum - se->avg.load_sum, 0);
}

#ifndef CONFIG_64BIT
static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
{
    u64 last_update_time_copy;
    u64 last_update_time;

    do {
        last_update_time_copy = cfs_rq->load_last_update_time_copy;
        smp_rmb();
        last_update_time = cfs_rq->avg.last_update_time;
    } while (last_update_time != last_update_time_copy);

    return last_update_time;
}
#else
static inline u64 cfs_rq_last_update_time(struct cfs_rq *cfs_rq)
{
    return cfs_rq->avg.last_update_time;
}
#endif

/*
 * Task first catches up with cfs_rq, and then subtract
 * itself from the cfs_rq (task must be off the queue now).
 */
void remove_entity_load_avg(struct sched_entity *se)
{
    struct cfs_rq *cfs_rq = cfs_rq_of(se);
    u64 last_update_time;

    /*
     * Newly created task or never used group entity should not be removed
     * from its (source) cfs_rq
     */
    if (se->avg.last_update_time == 0)
        return;

    last_update_time = cfs_rq_last_update_time(cfs_rq);

    __update_load_avg(last_update_time, cpu_of(rq_of(cfs_rq)), &se->avg, 0, 0, NULL);
    atomic_long_add(se->avg.load_avg, &cfs_rq->removed_load_avg);
    atomic_long_add(se->avg.util_avg, &cfs_rq->removed_util_avg);
}

static inline unsigned long cfs_rq_runnable_load_avg(struct cfs_rq *cfs_rq)
{
    return cfs_rq->runnable_load_avg;
}

static inline unsigned long cfs_rq_load_avg(struct cfs_rq *cfs_rq)
{
    return cfs_rq->avg.load_avg;
}

static int idle_balance(struct rq *this_rq);

#else /* CONFIG_SMP */

static inline void update_load_avg(struct sched_entity *se, int not_used)
{
    struct cfs_rq *cfs_rq = cfs_rq_of(se);
    struct rq *rq = rq_of(cfs_rq);

    cpufreq_trigger_update(rq_clock(rq));
}

static inline void
enqueue_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
static inline void
dequeue_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
static inline void remove_entity_load_avg(struct sched_entity *se) {}

static inline void
attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
static inline void
detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}

static inline int idle_balance(struct rq *rq)
{
    return 0;
}

#endif /* CONFIG_SMP */

static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
#ifdef CONFIG_SCHEDSTATS
    struct task_struct *tsk = NULL;

    if (entity_is_task(se))
        tsk = task_of(se);

    if (se->statistics.sleep_start) {
        u64 delta = rq_clock(rq_of(cfs_rq)) - se->statistics.sleep_start;

        if ((s64)delta < 0)
            delta = 0;

        if (unlikely(delta > se->statistics.sleep_max))
            se->statistics.sleep_max = delta;

        se->statistics.sleep_start = 0;
        se->statistics.sum_sleep_runtime += delta;

        if (tsk) {
            account_scheduler_latency(tsk, delta >> 10, 1);
            trace_sched_stat_sleep(tsk, delta);
        }
    }
    if (se->statistics.block_start) {
        u64 delta = rq_clock(rq_of(cfs_rq)) - se->statistics.block_start;

        if ((s64)delta < 0)
            delta = 0;

        if (unlikely(delta > se->statistics.block_max))
            se->statistics.block_max = delta;

        se->statistics.block_start = 0;
        se->statistics.sum_sleep_runtime += delta;

        if (tsk) {
            if (tsk->in_iowait) {
                se->statistics.iowait_sum += delta;
                se->statistics.iowait_count++;
                trace_sched_stat_iowait(tsk, delta);
            }

            trace_sched_stat_blocked(tsk, delta);

            /*
             * Blocking time is in units of nanosecs, so shift by
             * 20 to get a milliseconds-range estimation of the
             * amount of time that the task spent sleeping:
             */
            if (unlikely(prof_on == SLEEP_PROFILING)) {
                profile_hits(SLEEP_PROFILING,
                        (void *)get_wchan(tsk),
                        delta >> 20);
            }
            account_scheduler_latency(tsk, delta >> 10, 0);
        }
    }
#endif
}

static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
#ifdef CONFIG_SCHED_DEBUG
    s64 d = se->vruntime - cfs_rq->min_vruntime;

    if (d < 0)
        d = -d;

    if (d > 3*sysctl_sched_latency)
        schedstat_inc(cfs_rq, nr_spread_over);
#endif
}

static void
place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
{
    u64 vruntime = cfs_rq->min_vruntime;

    /*
     * The 'current' period is already promised to the current tasks,
     * however the extra weight of the new task will slow them down a
     * little, place the new task so that it fits in the slot that
     * stays open at the end.
     *
     * 如果是新进程第一次要入队, 那么就要初始化它的vruntime
     * 一般就把cfsq的vruntime给它就可以
     * 但是如果当前运行的所有进程被承诺了一个运行周期
     * 那么则将新进程的vruntime后推一个他自己的slice
     * 实际上新进程入队时要重新计算运行队列的总权值
     * 总权值显然是增加了，但是所有进程总的运行时期并不一定随之增加
     * 则每个进程的承诺时间相当于减小了，就是减慢了进程们的虚拟时钟步伐。 
     */
    /*  initial标识了该进程是新进程  */
    if (initial && sched_feat(START_DEBIT))
        vruntime += sched_vslice(cfs_rq, se);

    /* sleeps up to a single latency don't count. 
     * 休眠进程  */
    if (!initial)
    {
        /*  一个调度周期  */
        unsigned long thresh = sysctl_sched_latency;

        /*
         * Halve their sleep time's effect, to allow
         * for a gentler effect of sleepers:
         */
        /*  若设了GENTLE_FAIR_SLEEPERS  */
        if (sched_feat(GENTLE_FAIR_SLEEPERS))
            thresh >>= 1;   /*  补偿减为调度周期的一半  */

        vruntime -= thresh;
    }

    /* ensure we never gain time by being placed backwards.
     * 如果是唤醒已经存在的进程，则单调附值
     */
    se->vruntime = max_vruntime(se->vruntime, vruntime);
}

static void check_enqueue_throttle(struct cfs_rq *cfs_rq);

static inline void check_schedstat_required(void)
{
#ifdef CONFIG_SCHEDSTATS
    if (schedstat_enabled())
        return;

    /* Force schedstat enabled if a dependent tracepoint is active */
    if (trace_sched_stat_wait_enabled()    ||
            trace_sched_stat_sleep_enabled()   ||
            trace_sched_stat_iowait_enabled()  ||
            trace_sched_stat_blocked_enabled() ||
            trace_sched_stat_runtime_enabled())  {
        pr_warn_once("Scheduler tracepoints stat_sleep, stat_iowait, "
                 "stat_blocked and stat_runtime require the "
                 "kernel parameter schedstats=enabled or "
                 "kernel.sched_schedstats=1\n");
    }
#endif
}

static void
enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
    /*
     * Update the normalized vruntime before updating min_vruntime
     * through calling update_curr().
     *
     * 如果当前进程之前已经是可运行状态不是被唤醒的那么其虚拟运行时间要增加
     */
    if (!(flags & ENQUEUE_WAKEUP) || (flags & ENQUEUE_WAKING))
        se->vruntime += cfs_rq->min_vruntime;

    /*
     * Update run-time statistics of the 'current'.
     * 更新进程的统计量信息
     */
    update_curr(cfs_rq);
    enqueue_entity_load_avg(cfs_rq, se);
    account_entity_enqueue(cfs_rq, se);
    update_cfs_shares(cfs_rq);

    /*  如果当前进行之前在睡眠刚被唤醒  */
    if (flags & ENQUEUE_WAKEUP)
    {
        /*  调整进程的虚拟运行时间  */
        place_entity(cfs_rq, se, 0);    
        if (schedstat_enabled())
            enqueue_sleeper(cfs_rq, se);
    }

    check_schedstat_required();
    if (schedstat_enabled()) {
        update_stats_enqueue(cfs_rq, se);
        check_spread(cfs_rq, se);
    }

    /*  将进程插入到红黑树中  */
    if (se != cfs_rq->curr)
        __enqueue_entity(cfs_rq, se);
    se->on_rq = 1;

    if (cfs_rq->nr_running == 1) {
        list_add_leaf_cfs_rq(cfs_rq);
        check_enqueue_throttle(cfs_rq);
    }
}

static void __clear_buddies_last(struct sched_entity *se)
{
    for_each_sched_entity(se) {
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        if (cfs_rq->last != se)
            break;

        cfs_rq->last = NULL;
    }
}

static void __clear_buddies_next(struct sched_entity *se)
{
    for_each_sched_entity(se) {
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        if (cfs_rq->next != se)
            break;

        cfs_rq->next = NULL;
    }
}

static void __clear_buddies_skip(struct sched_entity *se)
{
    for_each_sched_entity(se) {
        struct cfs_rq *cfs_rq = cfs_rq_of(se);
        if (cfs_rq->skip != se)
            break;

        cfs_rq->skip = NULL;
    }
}

static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    if (cfs_rq->last == se)
        __clear_buddies_last(se);

    if (cfs_rq->next == se)
        __clear_buddies_next(se);

    if (cfs_rq->skip == se)
        __clear_buddies_skip(se);
}

static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);

static void
dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
    /*
     * Update run-time statistics of the 'current'.
     */
    update_curr(cfs_rq);
    dequeue_entity_load_avg(cfs_rq, se);

    if (schedstat_enabled())
        update_stats_dequeue(cfs_rq, se, flags);

    clear_buddies(cfs_rq, se);

    if (se != cfs_rq->curr)
        __dequeue_entity(cfs_rq, se);
    se->on_rq = 0;
    account_entity_dequeue(cfs_rq, se);

    /*
     * Normalize the entity after updating the min_vruntime because the
     * update can refer to the ->curr item and we need to reflect this
     * movement in our normalized position.
     */
    if (!(flags & DEQUEUE_SLEEP))
        se->vruntime -= cfs_rq->min_vruntime;

    /* return excess runtime on last dequeue */
    return_cfs_rq_runtime(cfs_rq);

    update_min_vruntime(cfs_rq);
    update_cfs_shares(cfs_rq);
}

/*
 * Preempt the current task with a newly woken task if needed:
 */
static void
check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
{
    unsigned long ideal_runtime, delta_exec;
    struct sched_entity *se;
    s64 delta;

    /*  计算curr的理论上应该运行的时间  */
    ideal_runtime = sched_slice(cfs_rq, curr);
    
    /*  计算curr的实际运行时间 
     *  sum_exec_runtime: 进程执行的总时间 
     *  prev_sum_exec_runtime:进程在切换进CPU时的sum_exec_runtime值*/
    delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime;
    
    /*  如果实际运行时间比理论上应该运行的时间长  
     *  说明curr进程已经运行了足够长的时间
     *  应该调度新的进程抢占CPU了  */
    if (delta_exec > ideal_runtime)
    {
        resched_curr(rq_of(cfs_rq));
        /*
         * The current task ran long enough, ensure it doesn't get
         * re-elected due to buddy favours.
         * 由于当前进程curr运行了足够时间
         * 就取消它在buddy中的优先权
         */
        clear_buddies(cfs_rq, curr);
        return;
    }

    /*
     * Ensure that a task that missed wakeup preemption by a
     * narrow margin doesn't have to wait for a full slice.
     * This also mitigates buddy induced latencies under load.
     * 下面是这里是第二个抢占条件
     * 红黑树中最做节点最小虚拟运行时间的进程和当前进程的虚拟运行时间进行比较， 
     * 如果后者比前者大了ideal_runtime，就需要进行调度
     * 此时说明curr进程已经领先其他进程
     * 红黑树中的其他进程接近于饥饿状态, 应该立即补偿
     */
    if (delta_exec < sysctl_sched_min_granularity)
        return;

    se = __pick_first_entity(cfs_rq);
    delta = curr->vruntime - se->vruntime;

    if (delta < 0)
        return;

    if (delta > ideal_runtime)
        resched_curr(rq_of(cfs_rq));
}

static void
set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
    /* 'current' is not kept within the tree. */
    if (se->on_rq)  /*  如果se尚在rq队列上  */
    {
        /*
         * Any task has to be enqueued before it get to execute on
         * a CPU. So account for the time it spent waiting on the
         * runqueue.
         */
        if (schedstat_enabled())
            update_stats_wait_end(cfs_rq, se);
        /*  将se从rq队列中删除  */
        __dequeue_entity(cfs_rq, se);
        update_load_avg(se, 1);
    }
    /*  新sched_entity中的exec_start字段为当前clock_task  */
    update_stats_curr_start(cfs_rq, se);
    /*  将se设置为curr进程  */
    cfs_rq->curr = se;
#ifdef CONFIG_SCHEDSTATS
    /*
     * Track our maximum slice length, if the CPU's load is at
     * least twice that of our own weight (i.e. dont track it
     * when there are only lesser-weight tasks around):
     */
    if (schedstat_enabled() && rq_of(cfs_rq)->load.weight >= 2*se->load.weight) {
        se->statistics.slice_max = max(se->statistics.slice_max,
            se->sum_exec_runtime - se->prev_sum_exec_runtime);
    }
#endif
    /*  //更新task上一次投入运行的从时间  */
    se->prev_sum_exec_runtime = se->sum_exec_runtime;
}

static int
wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se);

/*
 * Pick the next process, keeping these things in mind, in this order:
 * 1) keep things fair between processes/task groups
 * 2) pick the "next" process, since someone really wants that to run
 * 3) pick the "last" process, for cache locality
 * 4) do not run the "skip" process, if something else is available
 *
 *  1. 首先要确保任务组之间的公平, 这也是设置组的原因之一
 *  2. 其次, 挑选下一个合适的（优先级比较高的）进程
 *     因为它确实需要马上运行 
 *  3. 如果没有找到条件2中的进程
 *     那么为了保持良好的局部性
 *     则选中上一次执行的进程 
 *  4. 只要有任务存在, 就不要让CPU空转, 
 *     只有在没有进程的情况下才会让CPU运行idle进程
 */
static struct sched_entity *
pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
{
    /*  摘取红黑树最左边的进程  */
    struct sched_entity *left = __pick_first_entity(cfs_rq);
    struct sched_entity *se;

    /*
     * If curr is set we have to see if its left of the leftmost entity
     * still in the tree, provided there was anything in the tree at all.
     *
     * 如果
     * left == NULL  或者
     * curr != NULL curr进程比left进程更优(即curr的虚拟运行时间更小) 
     * 说明curr进程是自动放弃运行权利, 且其比最左进程更优
     * 因此将left指向了curr, 即curr是最优的进程
     */
    if (!left || (curr && entity_before(curr, left)))
    {
        left = curr;
    }

    /* se = left存储了cfs_rq队列中最优的那个进程  
     * 如果进程curr是一个自愿放弃CPU的进程(其比最左进程更优), 则取se = curr
     * 否则进程se就取红黑树中最左的进程left, 它必然是当前就绪队列上最优的
     */
    se = left; /* ideally we run the leftmost entity */

    /*
     * Avoid running the skip buddy, if running something else can
     * be done without getting too unfair.
     *
     * cfs_rq->skip存储了需要调过不参与调度的进程调度实体
     * 如果我们挑选出来的最优调度实体se正好是skip
     * 那么我们需要选择次优的调度实体se来进行调度
     * 由于之前的se = left = (curr before left) curr left
     * 则如果 se == curr == skip, 则选择left = __pick_first_entity进行即可
     * 否则则se == left == skip, 则选择次优的那个调度实体second
     */
    if (cfs_rq->skip == se)
    {
        struct sched_entity *second;

        if (se == curr) /* se == curr == skip选择最左的那个调度实体left  */
        {
            second = __pick_first_entity(cfs_rq);
        }
        else    /*  否则se == left == skip, 选择次优的调度实体second  */
        {
            /*  摘取红黑树上第二左的进程节点  */
            second = __pick_next_entity(se);
            /*  同时与left进程一样, 
             * 如果
             * second == NULL 没有次优的进程  或者
             * curr != NULL curr进程比left进程更优(即curr的虚拟运行时间更小) 
             * 说明curr进程比最second进程更优
             * 因此将second指向了curr, 即curr是最优的进程*/
            if (!second || (curr && entity_before(curr, second)))
                second = curr;
        }

        /*  判断left和second的vruntime的差距是否小于sysctl_sched_wakeup_granularity*/
        if (second && wakeup_preempt_entity(second, left) < 1)
            se = second;
    }

    /*
     * Prefer last buddy, try to return the CPU to a preempted task.
     *
     * 
     */
    if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1)
        se = cfs_rq->last;

    /*
     * Someone really wants this to run. If it's not unfair, run it.
     */
    if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
        se = cfs_rq->next;

    /* 用过一次任何一个next或者last
     * 都需要清除掉这个指针
     * 以免影响到下次pick next sched_entity  */
    clear_buddies(cfs_rq, se);

    return se;
}

static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq);

static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
{
    /*
     * If still on the runqueue then deactivate_task()
     * was not called and update_curr() has to be done:
     */
    if (prev->on_rq)
        update_curr(cfs_rq);

    /* throttle cfs_rqs exceeding runtime */
    check_cfs_rq_runtime(cfs_rq);

    if (schedstat_enabled()) {
        check_spread(cfs_rq, prev);
        if (prev->on_rq)
            update_stats_wait_start(cfs_rq, prev);
    }

    if (prev->on_rq) {
        /* Put 'current' back into the tree. */
        __enqueue_entity(cfs_rq, prev);
        /* in !on_rq case, update occurred at dequeue */
        update_load_avg(prev, 0);
    }
    cfs_rq->curr = NULL;
}

static void
entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
{
    /*
     * Update run-time statistics of the 'current'.
     */
    update_curr(cfs_rq);

    /*
     * Ensure that runnable average is periodically updated.
     */
    update_load_avg(curr, 1);
    update_cfs_shares(cfs_rq);

#ifdef CONFIG_SCHED_HRTICK
    /*
     * queued ticks are scheduled to match the slice, so don't bother
     * validating it and just reschedule.
     */
    if (queued) {
        resched_curr(rq_of(cfs_rq));
        return;
    }
    /*
     * don't let the period tick interfere with the hrtick preemption
     */
    if (!sched_feat(DOUBLE_TICK) &&
            hrtimer_active(&rq_of(cfs_rq)->hrtick_timer))
        return;
#endif

    if (cfs_rq->nr_running > 1)
        check_preempt_tick(cfs_rq, curr);
}


/**************************************************
 * CFS bandwidth control machinery
 */

#ifdef CONFIG_CFS_BANDWIDTH

#ifdef HAVE_JUMP_LABEL
static struct static_key __cfs_bandwidth_used;

static inline bool cfs_bandwidth_used(void)
{
    return static_key_false(&__cfs_bandwidth_used);
}

void cfs_bandwidth_usage_inc(void)
{
    static_key_slow_inc(&__cfs_bandwidth_used);
}

void cfs_bandwidth_usage_dec(void)
{
    static_key_slow_dec(&__cfs_bandwidth_used);
}
#else /* HAVE_JUMP_LABEL */
static bool cfs_bandwidth_used(void)
{
    return true;
}

void cfs_bandwidth_usage_inc(void) {}
void cfs_bandwidth_usage_dec(void) {}
#endif /* HAVE_JUMP_LABEL */

/*
 * default period for cfs group bandwidth.
 * default: 0.1s, units: nanoseconds
 */
static inline u64 default_cfs_period(void)
{
    return 100000000ULL;
}

static inline u64 sched_cfs_bandwidth_slice(void)
{
    return (u64)sysctl_sched_cfs_bandwidth_slice * NSEC_PER_USEC;
}

/*
 * Replenish runtime according to assigned quota and update expiration time.
 * We use sched_clock_cpu directly instead of rq->clock to avoid adding
 * additional synchronization around rq->lock.
 *
 * requires cfs_b->lock
 */
void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b)
{
    u64 now;

    if (cfs_b->quota == RUNTIME_INF)
        return;

    now = sched_clock_cpu(smp_processor_id());
    cfs_b->runtime = cfs_b->quota;
    cfs_b->runtime_expires = now + ktime_to_ns(cfs_b->period);
}

static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
{
    return &tg->cfs_bandwidth;
}

/* rq->task_clock normalized against any time this cfs_rq has spent throttled */
static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
{
    if (unlikely(cfs_rq->throttle_count))
        return cfs_rq->throttled_clock_task;

    return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
}

/* returns 0 on failure to allocate runtime */
static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
    struct task_group *tg = cfs_rq->tg;
    struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(tg);
    u64 amount = 0, min_amount, expires;

    /* note: this is a positive sum as runtime_remaining <= 0 */
    min_amount = sched_cfs_bandwidth_slice() - cfs_rq->runtime_remaining;

    raw_spin_lock(&cfs_b->lock);
    if (cfs_b->quota == RUNTIME_INF)
        amount = min_amount;
    else {
        start_cfs_bandwidth(cfs_b);

        if (cfs_b->runtime > 0) {
            amount = min(cfs_b->runtime, min_amount);
            cfs_b->runtime -= amount;
            cfs_b->idle = 0;
        }
    }
    expires = cfs_b->runtime_expires;
    raw_spin_unlock(&cfs_b->lock);

    cfs_rq->runtime_remaining += amount;
    /*
     * we may have advanced our local expiration to account for allowed
     * spread between our sched_clock and the one on which runtime was
     * issued.
     */
    if ((s64)(expires - cfs_rq->runtime_expires) > 0)
        cfs_rq->runtime_expires = expires;

    return cfs_rq->runtime_remaining > 0;
}

/*
 * Note: This depends on the synchronization provided by sched_clock and the
 * fact that rq->clock snapshots this value.
 */
static void expire_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
    struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);

    /* if the deadline is ahead of our clock, nothing to do */
    if (likely((s64)(rq_clock(rq_of(cfs_rq)) - cfs_rq->runtime_expires) < 0))
        return;

    if (cfs_rq->runtime_remaining < 0)
        return;

    /*
     * If the local deadline has passed we have to consider the
     * possibility that our sched_clock is 'fast' and the global deadline
     * has not truly expired.
     *
     * Fortunately we can check determine whether this the case by checking
     * whether the global deadline has advanced. It is valid to compare
     * cfs_b->runtime_expires without any locks since we only care about
     * exact equality, so a partial write will still work.
     */

    if (cfs_rq->runtime_expires != cfs_b->runtime_expires) {
        /* extend local deadline, drift is bounded above by 2 ticks */
        cfs_rq->runtime_expires += TICK_NSEC;
    } else {
        /* global deadline is ahead, expiration has passed */
        cfs_rq->runtime_remaining = 0;
    }
}

static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
{
    /* dock delta_exec before expiring quota (as it could span periods) */
    cfs_rq->runtime_remaining -= delta_exec;
    expire_cfs_rq_runtime(cfs_rq);

    if (likely(cfs_rq->runtime_remaining > 0))
        return;

    /*
     * if we're unable to extend our runtime we resched so that the active
     * hierarchy can be throttled
     */
    if (!assign_cfs_rq_runtime(cfs_rq) && likely(cfs_rq->curr))
        resched_curr(rq_of(cfs_rq));
}

static __always_inline
void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
{
    if (!cfs_bandwidth_used() || !cfs_rq->runtime_enabled)
        return;

    __account_cfs_rq_runtime(cfs_rq, delta_exec);
}

static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
{
    return cfs_bandwidth_used() && cfs_rq->throttled;
}

/* check whether cfs_rq, or any parent, is throttled */
static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
{
    return cfs_bandwidth_used() && cfs_rq->throttle_count;
}

/*
 * Ensure that neither of the group entities corresponding to src_cpu or
 * dest_cpu are members of a throttled hierarchy when performing group
 * load-balance operations.
 */
static inline int throttled_lb_pair(struct task_group *tg,
                    int src_cpu, int dest_cpu)
{
    struct cfs_rq *src_cfs_rq, *dest_cfs_rq;

    src_cfs_rq = tg->cfs_rq[src_cpu];
    dest_cfs_rq = tg->cfs_rq[dest_cpu];

    return throttled_hierarchy(src_cfs_rq) ||
           throttled_hierarchy(dest_cfs_rq);
}

/* updated child weight may affect parent so we have to do this bottom up */
static int tg_unthrottle_up(struct task_group *tg, void *data)
{
    struct rq *rq = data;
    struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];

    cfs_rq->throttle_count--;
#ifdef CONFIG_SMP
    if (!cfs_rq->throttle_count) {
        /* adjust cfs_rq_clock_task() */
        cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
                         cfs_rq->throttled_clock_task;
    }
#endif

    return 0;
}

static int tg_throttle_down(struct task_group *tg, void *data)
{
    struct rq *rq = data;
    struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];

    /* group is entering throttled state, stop time */
    if (!cfs_rq->throttle_count)
        cfs_rq->throttled_clock_task = rq_clock_task(rq);
    cfs_rq->throttle_count++;

    return 0;
}

static void throttle_cfs_rq(struct cfs_rq *cfs_rq)
{
    struct rq *rq = rq_of(cfs_rq);
    struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
    struct sched_entity *se;
    long task_delta, dequeue = 1;
    bool empty;

    se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];

    /* freeze hierarchy runnable averages while throttled */
    rcu_read_lock();
    walk_tg_tree_from(cfs_rq->tg, tg_throttle_down, tg_nop, (void *)rq);
    rcu_read_unlock();

    task_delta = cfs_rq->h_nr_running;
    for_each_sched_entity(se) {
        struct cfs_rq *qcfs_rq = cfs_rq_of(se);
        /* throttled entity or throttle-on-deactivate */
        if (!se->on_rq)
            break;

        if (dequeue)
            dequeue_entity(qcfs_rq, se, DEQUEUE_SLEEP);
        qcfs_rq->h_nr_running -= task_delta;

        if (qcfs_rq->load.weight)
            dequeue = 0;
    }

    if (!se)
        sub_nr_running(rq, task_delta);

    cfs_rq->throttled = 1;
    cfs_rq->throttled_clock = rq_clock(rq);
    raw_spin_lock(&cfs_b->lock);
    empty = list_empty(&cfs_b->throttled_cfs_rq);

    /*
     * Add to the _head_ of the list, so that an already-started
     * distribute_cfs_runtime will not see us
     */
    list_add_rcu(&cfs_rq->throttled_list, &cfs_b->throttled_cfs_rq);

    /*
     * If we're the first throttled task, make sure the bandwidth
     * timer is running.
     */
    if (empty)
        start_cfs_bandwidth(cfs_b);

    raw_spin_unlock(&cfs_b->lock);
}

void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
{
    struct rq *rq = rq_of(cfs_rq);
    struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
    struct sched_entity *se;
    int enqueue = 1;
    long task_delta;

    se = cfs_rq->tg->se[cpu_of(rq)];

    cfs_rq->throttled = 0;

    update_rq_clock(rq);

    raw_spin_lock(&cfs_b->lock);
    cfs_b->throttled_time += rq_clock(rq) - cfs_rq->throttled_clock;
    list_del_rcu(&cfs_rq->throttled_list);
    raw_spin_unlock(&cfs_b->lock);

    /* update hierarchical throttle state */
    walk_tg_tree_from(cfs_rq->tg, tg_nop, tg_unthrottle_up, (void *)rq);

    if (!cfs_rq->load.weight)
        return;

    task_delta = cfs_rq->h_nr_running;
    for_each_sched_entity(se) {
        if (se->on_rq)
            enqueue = 0;

        cfs_rq = cfs_rq_of(se);
        if (enqueue)
            enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
        cfs_rq->h_nr_running += task_delta;

        if (cfs_rq_throttled(cfs_rq))
            break;
    }

    if (!se)
        add_nr_running(rq, task_delta);

    /* determine whether we need to wake up potentially idle cpu */
    if (rq->curr == rq->idle && rq->cfs.nr_running)
        resched_curr(rq);
}

static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
        u64 remaining, u64 expires)
{
    struct cfs_rq *cfs_rq;
    u64 runtime;
    u64 starting_runtime = remaining;

    rcu_read_lock();
    list_for_each_entry_rcu(cfs_rq, &cfs_b->throttled_cfs_rq,
                throttled_list) {
        struct rq *rq = rq_of(cfs_rq);

        raw_spin_lock(&rq->lock);
        if (!cfs_rq_throttled(cfs_rq))
            goto next;

        runtime = -cfs_rq->runtime_remaining + 1;
        if (runtime > remaining)
            runtime = remaining;
        remaining -= runtime;

        cfs_rq->runtime_remaining += runtime;
        cfs_rq->runtime_expires = expires;

        /* we check whether we're throttled above */
        if (cfs_rq->runtime_remaining > 0)
            unthrottle_cfs_rq(cfs_rq);

next:
        raw_spin_unlock(&rq->lock);

        if (!remaining)
            break;
    }
    rcu_read_unlock();

    return starting_runtime - remaining;
}

/*
 * Responsible for refilling a task_group's bandwidth and unthrottling its
 * cfs_rqs as appropriate. If there has been no activity within the last
 * period the timer is deactivated until scheduling resumes; cfs_b->idle is
 * used to track this state.
 */
static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
{
    u64 runtime, runtime_expires;
    int throttled;

    /* no need to continue the timer with no bandwidth constraint */
    if (cfs_b->quota == RUNTIME_INF)
        goto out_deactivate;

    throttled = !list_empty(&cfs_b->throttled_cfs_rq);
    cfs_b->nr_periods += overrun;

    /*
     * idle depends on !throttled (for the case of a large deficit), and if
     * we're going inactive then everything else can be deferred
     */
    if (cfs_b->idle && !throttled)
        goto out_deactivate;

    __refill_cfs_bandwidth_runtime(cfs_b);

    if (!throttled) {
        /* mark as potentially idle for the upcoming period */
        cfs_b->idle = 1;
        return 0;
    }

    /* account preceding periods in which throttling occurred */
    cfs_b->nr_throttled += overrun;

    runtime_expires = cfs_b->runtime_expires;

    /*
     * This check is repeated as we are holding onto the new bandwidth while
     * we unthrottle. This can potentially race with an unthrottled group
     * trying to acquire new bandwidth from the global pool. This can result
     * in us over-using our runtime if it is all used during this loop, but
     * only by limited amounts in that extreme case.
     */
    while (throttled && cfs_b->runtime > 0) {
        runtime = cfs_b->runtime;
        raw_spin_unlock(&cfs_b->lock);
        /* we can't nest cfs_b->lock while distributing bandwidth */
        runtime = distribute_cfs_runtime(cfs_b, runtime,
                         runtime_expires);
        raw_spin_lock(&cfs_b->lock);

        throttled = !list_empty(&cfs_b->throttled_cfs_rq);

        cfs_b->runtime -= min(runtime, cfs_b->runtime);
    }

    /*
     * While we are ensured activity in the period following an
     * unthrottle, this also covers the case in which the new bandwidth is
     * insufficient to cover the existing bandwidth deficit.  (Forcing the
     * timer to remain active while there are any throttled entities.)
     */
    cfs_b->idle = 0;

    return 0;

out_deactivate:
    return 1;
}

/* a cfs_rq won't donate quota below this amount */
static const u64 min_cfs_rq_runtime = 1 * NSEC_PER_MSEC;
/* minimum remaining period time to redistribute slack quota */
static const u64 min_bandwidth_expiration = 2 * NSEC_PER_MSEC;
/* how long we wait to gather additional slack before distributing */
static const u64 cfs_bandwidth_slack_period = 5 * NSEC_PER_MSEC;

/*
 * Are we near the end of the current quota period?
 *
 * Requires cfs_b->lock for hrtimer_expires_remaining to be safe against the
 * hrtimer base being cleared by hrtimer_start. In the case of
 * migrate_hrtimers, base is never cleared, so we are fine.
 */
static int runtime_refresh_within(struct cfs_bandwidth *cfs_b, u64 min_expire)
{
    struct hrtimer *refresh_timer = &cfs_b->period_timer;
    u64 remaining;

    /* if the call-back is running a quota refresh is already occurring */
    if (hrtimer_callback_running(refresh_timer))
        return 1;

    /* is a quota refresh about to occur? */
    remaining = ktime_to_ns(hrtimer_expires_remaining(refresh_timer));
    if (remaining < min_expire)
        return 1;

    return 0;
}

static void start_cfs_slack_bandwidth(struct cfs_bandwidth *cfs_b)
{
    u64 min_left = cfs_bandwidth_slack_period + min_bandwidth_expiration;

    /* if there's a quota refresh soon don't bother with slack */
    if (runtime_refresh_within(cfs_b, min_left))
        return;

    hrtimer_start(&cfs_b->slack_timer,
            ns_to_ktime(cfs_bandwidth_slack_period),
            HRTIMER_MODE_REL);
}

/* we know any runtime found here is valid as update_curr() precedes return */
static void __return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
    struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
    s64 slack_runtime = cfs_rq->runtime_remaining - min_cfs_rq_runtime;

    if (slack_runtime <= 0)
        return;

    raw_spin_lock(&cfs_b->lock);
    if (cfs_b->quota != RUNTIME_INF &&
        cfs_rq->runtime_expires == cfs_b->runtime_expires) {
        cfs_b->runtime += slack_runtime;

        /* we are under rq->lock, defer unthrottling using a timer */
        if (cfs_b->runtime > sched_cfs_bandwidth_slice() &&
            !list_empty(&cfs_b->throttled_cfs_rq))
            start_cfs_slack_bandwidth(cfs_b);
    }
    raw_spin_unlock(&cfs_b->lock);

    /* even if it's not valid for return we don't want to try again */
    cfs_rq->runtime_remaining -= slack_runtime;
}

static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
    if (!cfs_bandwidth_used())
        return;

    if (!cfs_rq->runtime_enabled || cfs_rq->nr_running)
        return;

    __return_cfs_rq_runtime(cfs_rq);
}

/*
 * This is done with a timer (instead of inline with bandwidth return) since
 * it's necessary to juggle rq->locks to unthrottle their respective cfs_rqs.
 */
static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
{
    u64 runtime = 0, slice = sched_cfs_bandwidth_slice();
    u64 expires;

    /* confirm we're still not at a refresh boundary */
    raw_spin_lock(&cfs_b->lock);
    if (runtime_refresh_within(cfs_b, min_bandwidth_expiration)) {
        raw_spin_unlock(&cfs_b->lock);
        return;
    }

    if (cfs_b->quota != RUNTIME_INF && cfs_b->runtime > slice)
        runtime = cfs_b->runtime;

    expires = cfs_b->runtime_expires;
    raw_spin_unlock(&cfs_b->lock);

    if (!runtime)
        return;

    runtime = distribute_cfs_runtime(cfs_b, runtime, expires);

    raw_spin_lock(&cfs_b->lock);
    if (expires == cfs_b->runtime_expires)
        cfs_b->runtime -= min(runtime, cfs_b->runtime);
    raw_spin_unlock(&cfs_b->lock);
}

/*
 * When a group wakes up we want to make sure that its quota is not already
 * expired/exceeded, otherwise it may be allowed to steal additional ticks of
 * runtime as update_curr() throttling can not not trigger until it's on-rq.
 */
static void check_enqueue_throttle(struct cfs_rq *cfs_rq)
{
    if (!cfs_bandwidth_used())
        return;

    /* an active group must be handled by the update_curr()->put() path */
    if (!cfs_rq->runtime_enabled || cfs_rq->curr)
        return;

    /* ensure the group is not already throttled */
    if (cfs_rq_throttled(cfs_rq))
        return;

    /* update runtime allocation */
    account_cfs_rq_runtime(cfs_rq, 0);
    if (cfs_rq->runtime_remaining <= 0)
        throttle_cfs_rq(cfs_rq);
}

/* conditionally throttle active cfs_rq's from put_prev_entity() */
static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
    if (!cfs_bandwidth_used())
        return false;

    if (likely(!cfs_rq->runtime_enabled || cfs_rq->runtime_remaining > 0))
        return false;

    /*
     * it's possible for a throttled entity to be forced into a running
     * state (e.g. set_curr_task), in this case we're finished.
     */
    if (cfs_rq_throttled(cfs_rq))
        return true;

    throttle_cfs_rq(cfs_rq);
    return true;
}

static enum hrtimer_restart sched_cfs_slack_timer(struct hrtimer *timer)
{
    struct cfs_bandwidth *cfs_b =
        container_of(timer, struct cfs_bandwidth, slack_timer);

    do_sched_cfs_slack_timer(cfs_b);

    return HRTIMER_NORESTART;
}

static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
{
    struct cfs_bandwidth *cfs_b =
        container_of(timer, struct cfs_bandwidth, period_timer);
    int overrun;
    int idle = 0;

    raw_spin_lock(&cfs_b->lock);
    for (;;) {
        overrun = hrtimer_forward_now(timer, cfs_b->period);
        if (!overrun)
            break;

        idle = do_sched_cfs_period_timer(cfs_b, overrun);
    }
    if (idle)
        cfs_b->period_active = 0;
    raw_spin_unlock(&cfs_b->lock);

    return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
}

void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
{
    raw_spin_lock_init(&cfs_b->lock);
    cfs_b->runtime = 0;
    cfs_b->quota = RUNTIME_INF;
    cfs_b->period = ns_to_ktime(default_cfs_period());

    INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
    hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
    cfs_b->period_timer.function = sched_cfs_period_timer;
    hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
    cfs_b->slack_timer.function = sched_cfs_slack_timer;
}

static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
    cfs_rq->runtime_enabled = 0;
    INIT_LIST_HEAD(&cfs_rq->throttled_list);
}

void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
{
    lockdep_assert_held(&cfs_b->lock);

    if (!cfs_b->period_active) {
        cfs_b->period_active = 1;
        hrtimer_forward_now(&cfs_b->period_timer, cfs_b->period);
        hrtimer_start_expires(&cfs_b->period_timer, HRTIMER_MODE_ABS_PINNED);
    }
}

static void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
{
    /* init_cfs_bandwidth() was not called */
    if (!cfs_b->throttled_cfs_rq.next)
        return;

    hrtimer_cancel(&cfs_b->period_timer);
    hrtimer_cancel(&cfs_b->slack_timer);
}

static void __maybe_unused update_runtime_enabled(struct rq *rq)
{
    struct cfs_rq *cfs_rq;

    for_each_leaf_cfs_rq(rq, cfs_rq) {
        struct cfs_bandwidth *cfs_b = &cfs_rq->tg->cfs_bandwidth;

        raw_spin_lock(&cfs_b->lock);
        cfs_rq->runtime_enabled = cfs_b->quota != RUNTIME_INF;
        raw_spin_unlock(&cfs_b->lock);
    }
}

static void __maybe_unused unthrottle_offline_cfs_rqs(struct rq *rq)
{
    struct cfs_rq *cfs_rq;

    for_each_leaf_cfs_rq(rq, cfs_rq) {
        if (!cfs_rq->runtime_enabled)
            continue;

        /*
         * clock_task is not advancing so we just need to make sure
         * there's some valid quota amount
         */
        cfs_rq->runtime_remaining = 1;
        /*
         * Offline rq is schedulable till cpu is completely disabled
         * in take_cpu_down(), so we prevent new cfs throttling here.
         */
        cfs_rq->runtime_enabled = 0;

        if (cfs_rq_throttled(cfs_rq))
            unthrottle_cfs_rq(cfs_rq);
    }
}

#else /* CONFIG_CFS_BANDWIDTH */
static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
{
    return rq_clock_task(rq_of(cfs_rq));
}

static void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec) {}
static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq) { return false; }
static void check_enqueue_throttle(struct cfs_rq *cfs_rq) {}
static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}

static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
{
    return 0;
}

static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
{
    return 0;
}

static inline int throttled_lb_pair(struct task_group *tg,
                    int src_cpu, int dest_cpu)
{
    return 0;
}

void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}

#ifdef CONFIG_FAIR_GROUP_SCHED
static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
#endif

static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
{
    return NULL;
}
static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {}
static inline void update_runtime_enabled(struct rq *rq) {}
static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {}

#endif /* CONFIG_CFS_BANDWIDTH */

/**************************************************
 * CFS operations on tasks:
 */

#ifdef CONFIG_SCHED_HRTICK
static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
{
    struct sched_entity *se = &p->se;
    struct cfs_rq *cfs_rq = cfs_rq_of(se);

    WARN_ON(task_rq(p) != rq);

    if (cfs_rq->nr_running > 1) {
        u64 slice = sched_slice(cfs_rq, se);
        u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
        s64 delta = slice - ran;

        if (delta < 0) {
            if (rq->curr == p)
                resched_curr(rq);
            return;
        }
        hrtick_start(rq, delta);
    }
}

/*
 * called from enqueue/dequeue and updates the hrtick when the
 * current task is from our class and nr_running is low enough
 * to matter.
 */
static void hrtick_update(struct rq *rq)
{
    struct task_struct *curr = rq->curr;

    if (!hrtick_enabled(rq) || curr->sched_class != &fair_sched_class)
        return;

    if (cfs_rq_of(&curr->se)->nr_running < sched_nr_latency)
        hrtick_start_fair(rq, curr);
}
#else /* !CONFIG_SCHED_HRTICK */
static inline void
hrtick_start_fair(struct rq *rq, struct task_struct *p)
{
}

static inline void hrtick_update(struct rq *rq)
{
}
#endif

/*
 * The enqueue_task method is called before nr_running is
 * increased. Here we update the fair scheduling stats and
 * then put the task into the rbtree:
 */
static void
enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
{
    struct cfs_rq *cfs_rq;
    struct sched_entity *se = &p->se;

    for_each_sched_entity(se) {
        if (se->on_rq)
            break;
        cfs_rq = cfs_rq_of(se);
        enqueue_entity(cfs_rq, se, flags);

        /*
         * end evaluation on encountering a throttled cfs_rq
         *
         * note: in the case of encountering a throttled cfs_rq we will
         * post the final h_nr_running increment below.
        */
        if (cfs_rq_throttled(cfs_rq))
            break;
        cfs_rq->h_nr_running++;

        flags = ENQUEUE_WAKEUP;
    }

    for_each_sched_entity(se) {
        cfs_rq = cfs_rq_of(se);
        cfs_rq->h_nr_running++;

        if (cfs_rq_throttled(cfs_rq))
            break;

        update_load_avg(se, 1);
        update_cfs_shares(cfs_rq);
    }

    if (!se)
        add_nr_running(rq, 1);

    hrtick_update(rq);
}

static void set_next_buddy(struct sched_entity *se);

/*
 * The dequeue_task method is called before nr_running is
 * decreased. We remove the task from the rbtree and
 * update the fair scheduling stats:
 */
static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
{
    struct cfs_rq *cfs_rq;
    struct sched_entity *se = &p->se;
    int task_sleep = flags & DEQUEUE_SLEEP;

    for_each_sched_entity(se) {
        cfs_rq = cfs_rq_of(se);
        /*  */
        dequeue_entity(cfs_rq, se, flags);

        /*
         * end evaluation on encountering a throttled cfs_rq
         *
         * note: in the case of encountering a throttled cfs_rq we will
         * post the final h_nr_running decrement below.
        */
        if (cfs_rq_throttled(cfs_rq))
            break;
        cfs_rq->h_nr_running--;

        /* Don't dequeue parent if it has other entities besides us */
        if (cfs_rq->load.weight) {
            /*
             * Bias pick_next to pick a task from this cfs_rq, as
             * p is sleeping when it is within its sched_slice.
             */
            if (task_sleep && parent_entity(se))
                set_next_buddy(parent_entity(se));

            /* avoid re-evaluating load for this entity */
            se = parent_entity(se);
            break;
        }
        flags |= DEQUEUE_SLEEP;
    }

    for_each_sched_entity(se) {
        cfs_rq = cfs_rq_of(se);
        cfs_rq->h_nr_running--;

        if (cfs_rq_throttled(cfs_rq))
            break;

        update_load_avg(se, 1);
        update_cfs_shares(cfs_rq);
    }

    if (!se)
        sub_nr_running(rq, 1);

    hrtick_update(rq);
}

#ifdef CONFIG_SMP

/*
 * per rq 'load' arrray crap; XXX kill this.
 */

/*
 * The exact cpuload calculated at every tick would be:
 *
 *   load' = (1 - 1/2^i) * load + (1/2^i) * cur_load
 *
 * If a cpu misses updates for n ticks (as it was idle) and update gets
 * called on the n+1-th tick when cpu may be busy, then we have:
 *
 *   load_n   = (1 - 1/2^i)^n * load_0
 *   load_n+1 = (1 - 1/2^i)   * load_n + (1/2^i) * cur_load
 *
 * decay_load_missed() below does efficient calculation of
 *
 *   load' = (1 - 1/2^i)^n * load
 *
 * Because x^(n+m) := x^n * x^m we can decompose any x^n in power-of-2 factors.
 * This allows us to precompute the above in said factors, thereby allowing the
 * reduction of an arbitrary n in O(log_2 n) steps. (See also
 * fixed_power_int())
 *
 * The calculation is approximated on a 128 point scale.
 */
#define DEGRADE_SHIFT       7

static const u8 degrade_zero_ticks[CPU_LOAD_IDX_MAX] = {0, 8, 32, 64, 128};
static const u8 degrade_factor[CPU_LOAD_IDX_MAX][DEGRADE_SHIFT + 1] = {
    {   0,   0,  0,  0,  0,  0, 0, 0 },
    {  64,  32,  8,  0,  0,  0, 0, 0 },
    {  96,  72, 40, 12,  1,  0, 0, 0 },
    { 112,  98, 75, 43, 15,  1, 0, 0 },
    { 120, 112, 98, 76, 45, 16, 2, 0 }
};

/*
 * Update cpu_load for any missed ticks, due to tickless idle. The backlog
 * would be when CPU is idle and so we just decay the old load without
 * adding any new load.
 */
static unsigned long
decay_load_missed(unsigned long load, unsigned long missed_updates, int idx)
{
    int j = 0;

    if (!missed_updates)
        return load;

    if (missed_updates >= degrade_zero_ticks[idx])
        return 0;

    if (idx == 1)
        return load >> missed_updates;

    while (missed_updates) {
        if (missed_updates % 2)
            load = (load * degrade_factor[idx][j]) >> DEGRADE_SHIFT;

        missed_updates >>= 1;
        j++;
    }
    return load;
}

/**
 * __update_cpu_load - update the rq->cpu_load[] statistics
 * @this_rq: The rq to update statistics for
 * @this_load: The current load
 * @pending_updates: The number of missed updates
 * @active: !0 for NOHZ_FULL
 *
 * Update rq->cpu_load[] statistics. This function is usually called every
 * scheduler tick (TICK_NSEC).
 *
 * This function computes a decaying average:
 *
 *   load[i]' = (1 - 1/2^i) * load[i] + (1/2^i) * load
 *
 * Because of NOHZ it might not get called on every tick which gives need for
 * the @pending_updates argument.
 *
 *   load[i]_n = (1 - 1/2^i) * load[i]_n-1 + (1/2^i) * load_n-1
 *         = A * load[i]_n-1 + B ; A := (1 - 1/2^i), B := (1/2^i) * load
 *         = A * (A * load[i]_n-2 + B) + B
 *         = A * (A * (A * load[i]_n-3 + B) + B) + B
 *         = A^3 * load[i]_n-3 + (A^2 + A + 1) * B
 *         = A^n * load[i]_0 + (A^(n-1) + A^(n-2) + ... + 1) * B
 *         = A^n * load[i]_0 + ((1 - A^n) / (1 - A)) * B
 *         = (1 - 1/2^i)^n * (load[i]_0 - load) + load
 *
 * In the above we've assumed load_n := load, which is true for NOHZ_FULL as
 * any change in load would have resulted in the tick being turned back on.
 *
 * For regular NOHZ, this reduces to:
 *
 *   load[i]_n = (1 - 1/2^i)^n * load[i]_0
 *
 * see decay_load_misses(). For NOHZ_FULL we get to subtract and add the extra
 * term. See the @active paramter.
 */
static void __update_cpu_load(struct rq *this_rq, unsigned long this_load,
                  unsigned long pending_updates, int active)
{
    unsigned long tickless_load = active ? this_rq->cpu_load[0] : 0;
    int i, scale;

    this_rq->nr_load_updates++;

    /* Update our load: */
    this_rq->cpu_load[0] = this_load; /* Fasttrack for idx 0 */
    for (i = 1, scale = 2; i < CPU_LOAD_IDX_MAX; i++, scale += scale) {
        unsigned long old_load, new_load;

        /* scale is effectively 1 << i now, and >> i divides by scale */

        old_load = this_rq->cpu_load[i];
        old_load = decay_load_missed(old_load, pending_updates - 1, i);
        if (tickless_load) {
            old_load -= decay_load_missed(tickless_load, pending_updates - 1, i);
            /*
             * old_load can never be a negative value because a
             * decayed tickless_load cannot be greater than the
             * original tickless_load.
             */
            old_load += tickless_load;
        }
        new_load = this_load;
        /*
         * Round up the averaging division if load is increasing. This
         * prevents us from getting stuck on 9 if the load is 10, for
         * example.
         */
        if (new_load > old_load)
            new_load += scale - 1;

        this_rq->cpu_load[i] = (old_load * (scale - 1) + new_load) >> i;
    }

    sched_avg_update(this_rq);
}

/* Used instead of source_load when we know the type == 0 */
static unsigned long weighted_cpuload(const int cpu)
{
    return cfs_rq_runnable_load_avg(&cpu_rq(cpu)->cfs);
}

#ifdef CONFIG_NO_HZ_COMMON
static void __update_cpu_load_nohz(struct rq *this_rq,
                   unsigned long curr_jiffies,
                   unsigned long load,
                   int active)
{
    unsigned long pending_updates;

    pending_updates = curr_jiffies - this_rq->last_load_update_tick;
    if (pending_updates) {
        this_rq->last_load_update_tick = curr_jiffies;
        /*
         * In the regular NOHZ case, we were idle, this means load 0.
         * In the NOHZ_FULL case, we were non-idle, we should consider
         * its weighted load.
         */
        __update_cpu_load(this_rq, load, pending_updates, active);
    }
}

/*
 * There is no sane way to deal with nohz on smp when using jiffies because the
 * cpu doing the jiffies update might drift wrt the cpu doing the jiffy reading
 * causing off-by-one errors in observed deltas; {0,2} instead of {1,1}.
 *
 * Therefore we cannot use the delta approach from the regular tick since that
 * would seriously skew the load calculation. However we'll make do for those
 * updates happening while idle (nohz_idle_balance) or coming out of idle
 * (tick_nohz_idle_exit).
 *
 * This means we might still be one tick off for nohz periods.
 */

/*
 * Called from nohz_idle_balance() to update the load ratings before doing the
 * idle balance.
 */
static void update_cpu_load_idle(struct rq *this_rq)
{
    /*
     * bail if there's load or we're actually up-to-date.
     */
    if (weighted_cpuload(cpu_of(this_rq)))
        return;

    __update_cpu_load_nohz(this_rq, READ_ONCE(jiffies), 0, 0);
}

/*
 * Called from tick_nohz_idle_exit() -- try and fix up the ticks we missed.
 */
void update_cpu_load_nohz(int active)
{
    struct rq *this_rq = this_rq();
    unsigned long curr_jiffies = READ_ONCE(jiffies);
    unsigned long load = active ? weighted_cpuload(cpu_of(this_rq)) : 0;

    if (curr_jiffies == this_rq->last_load_update_tick)
        return;

    raw_spin_lock(&this_rq->lock);
    __update_cpu_load_nohz(this_rq, curr_jiffies, load, active);
    raw_spin_unlock(&this_rq->lock);
}
#endif /* CONFIG_NO_HZ */

/*
 * Called from scheduler_tick()
 */
void update_cpu_load_active(struct rq *this_rq)
{
    unsigned long load = weighted_cpuload(cpu_of(this_rq));
    /*
     * See the mess around update_cpu_load_idle() / update_cpu_load_nohz().
     */
    this_rq->last_load_update_tick = jiffies;
    __update_cpu_load(this_rq, load, 1, 1);
}

/*
 * Return a low guess at the load of a migration-source cpu weighted
 * according to the scheduling class and "nice" value.
 *
 * We want to under-estimate the load of migration sources, to
 * balance conservatively.
 */
static unsigned long source_load(int cpu, int type)
{
    struct rq *rq = cpu_rq(cpu);
    unsigned long total = weighted_cpuload(cpu);

    if (type == 0 || !sched_feat(LB_BIAS))
        return total;

    return min(rq->cpu_load[type-1], total);
}

/*
 * Return a high guess at the load of a migration-target cpu weighted
 * according to the scheduling class and "nice" value.
 */
static unsigned long target_load(int cpu, int type)
{
    struct rq *rq = cpu_rq(cpu);
    unsigned long total = weighted_cpuload(cpu);

    if (type == 0 || !sched_feat(LB_BIAS))
        return total;

    return max(rq->cpu_load[type-1], total);
}

static unsigned long capacity_of(int cpu)
{
    return cpu_rq(cpu)->cpu_capacity;
}

static unsigned long capacity_orig_of(int cpu)
{
    return cpu_rq(cpu)->cpu_capacity_orig;
}

static unsigned long cpu_avg_load_per_task(int cpu)
{
    struct rq *rq = cpu_rq(cpu);
    unsigned long nr_running = READ_ONCE(rq->cfs.h_nr_running);
    unsigned long load_avg = weighted_cpuload(cpu);

    if (nr_running)
        return load_avg / nr_running;

    return 0;
}

static void record_wakee(struct task_struct *p)
{
    /*
     * Rough decay (wiping) for cost saving, don't worry
     * about the boundary, really active task won't care
     * about the loss.
     */
    if (time_after(jiffies, current->wakee_flip_decay_ts + HZ)) {
        current->wakee_flips >>= 1;
        current->wakee_flip_decay_ts = jiffies;
    }

    if (current->last_wakee != p) {
        current->last_wakee = p;
        current->wakee_flips++;
    }
}

static void task_waking_fair(struct task_struct *p)
{
    struct sched_entity *se = &p->se;
    struct cfs_rq *cfs_rq = cfs_rq_of(se);
    u64 min_vruntime;

#ifndef CONFIG_64BIT
    u64 min_vruntime_copy;

    do {
        min_vruntime_copy = cfs_rq->min_vruntime_copy;
        smp_rmb();
        min_vruntime = cfs_rq->min_vruntime;
    } while (min_vruntime != min_vruntime_copy);
#else
    min_vruntime = cfs_rq->min_vruntime;
#endif

    se->vruntime -= min_vruntime;
    record_wakee(p);
}

#ifdef CONFIG_FAIR_GROUP_SCHED
/*
 * effective_load() calculates the load change as seen from the root_task_group
 *
 * Adding load to a group doesn't make a group heavier, but can cause movement
 * of group shares between cpus. Assuming the shares were perfectly aligned one
 * can calculate the shift in shares.
 *
 * Calculate the effective load difference if @wl is added (subtracted) to @tg
 * on this @cpu and results in a total addition (subtraction) of @wg to the
 * total group weight.
 *
 * Given a runqueue weight distribution (rw_i) we can compute a shares
 * distribution (s_i) using:
 *
 *   s_i = rw_i / \Sum rw_j                         (1)
 *
 * Suppose we have 4 CPUs and our @tg is a direct child of the root group and
 * has 7 equal weight tasks, distributed as below (rw_i), with the resulting
 * shares distribution (s_i):
 *
 *   rw_i = {   2,   4,   1,   0 }
 *   s_i  = { 2/7, 4/7, 1/7,   0 }
 *
 * As per wake_affine() we're interested in the load of two CPUs (the CPU the
 * task used to run on and the CPU the waker is running on), we need to
 * compute the effect of waking a task on either CPU and, in case of a sync
 * wakeup, compute the effect of the current task going to sleep.
 *
 * So for a change of @wl to the local @cpu with an overall group weight change
 * of @wl we can compute the new shares distribution (s'_i) using:
 *
 *   s'_i = (rw_i + @wl) / (@wg + \Sum rw_j)                (2)
 *
 * Suppose we're interested in CPUs 0 and 1, and want to compute the load
 * differences in waking a task to CPU 0. The additional task changes the
 * weight and shares distributions like:
 *
 *   rw'_i = {   3,   4,   1,   0 }
 *   s'_i  = { 3/8, 4/8, 1/8,   0 }
 *
 * We can then compute the difference in effective weight by using:
 *
 *   dw_i = S * (s'_i - s_i)                        (3)
 *
 * Where 'S' is the group weight as seen by its parent.
 *
 * Therefore the effective change in loads on CPU 0 would be 5/56 (3/8 - 2/7)
 * times the weight of the group. The effect on CPU 1 would be -4/56 (4/8 -
 * 4/7) times the weight of the group.
 */
static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
{
    struct sched_entity *se = tg->se[cpu];

    if (!tg->parent)    /* the trivial, non-cgroup case */
        return wl;

    for_each_sched_entity(se) {
        long w, W;

        tg = se->my_q->tg;

        /*
         * W = @wg + \Sum rw_j
         */
        W = wg + calc_tg_weight(tg, se->my_q);

        /*
         * w = rw_i + @wl
         */
        w = cfs_rq_load_avg(se->my_q) + wl;

        /*
         * wl = S * s'_i; see (2)
         */
        if (W > 0 && w < W)
            wl = (w * (long)tg->shares) / W;
        else
            wl = tg->shares;

        /*
         * Per the above, wl is the new se->load.weight value; since
         * those are clipped to [MIN_SHARES, ...) do so now. See
         * calc_cfs_shares().
         */
        if (wl < MIN_SHARES)
            wl = MIN_SHARES;

        /*
         * wl = dw_i = S * (s'_i - s_i); see (3)
         */
        wl -= se->avg.load_avg;

        /*
         * Recursively apply this logic to all parent groups to compute
         * the final effective load change on the root group. Since
         * only the @tg group gets extra weight, all parent groups can
         * only redistribute existing shares. @wl is the shift in shares
         * resulting from this level per the above.
         */
        wg = 0;
    }

    return wl;
}
#else

static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
{
    return wl;
}

#endif

/*
 * Detect M:N waker/wakee relationships via a switching-frequency heuristic.
 * A waker of many should wake a different task than the one last awakened
 * at a frequency roughly N times higher than one of its wakees.  In order
 * to determine whether we should let the load spread vs consolodating to
 * shared cache, we look for a minimum 'flip' frequency of llc_size in one
 * partner, and a factor of lls_size higher frequency in the other.  With
 * both conditions met, we can be relatively sure that the relationship is
 * non-monogamous, with partner count exceeding socket size.  Waker/wakee
 * being client/server, worker/dispatcher, interrupt source or whatever is
 * irrelevant, spread criteria is apparent partner count exceeds socket size.
 */
static int wake_wide(struct task_struct *p)
{
    unsigned int master = current->wakee_flips;
    unsigned int slave = p->wakee_flips;
    int factor = this_cpu_read(sd_llc_size);

    if (master < slave)
        swap(master, slave);
    if (slave < factor || master < slave * factor)
        return 0;
    return 1;
}

static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
{
    s64 this_load, load;
    s64 this_eff_load, prev_eff_load;
    int idx, this_cpu, prev_cpu;
    struct task_group *tg;
    unsigned long weight;
    int balanced;

    idx       = sd->wake_idx;
    this_cpu  = smp_processor_id();
    prev_cpu  = task_cpu(p);
    load      = source_load(prev_cpu, idx);
    this_load = target_load(this_cpu, idx);

    /*
     * If sync wakeup then subtract the (maximum possible)
     * effect of the currently running task from the load
     * of the current CPU:
     */
    if (sync) {
        tg = task_group(current);
        weight = current->se.avg.load_avg;

        this_load += effective_load(tg, this_cpu, -weight, -weight);
        load += effective_load(tg, prev_cpu, 0, -weight);
    }

    tg = task_group(p);
    weight = p->se.avg.load_avg;

    /*
     * In low-load situations, where prev_cpu is idle and this_cpu is idle
     * due to the sync cause above having dropped this_load to 0, we'll
     * always have an imbalance, but there's really nothing you can do
     * about that, so that's good too.
     *
     * Otherwise check if either cpus are near enough in load to allow this
     * task to be woken on this_cpu.
     */
    this_eff_load = 100;
    this_eff_load *= capacity_of(prev_cpu);

    prev_eff_load = 100 + (sd->imbalance_pct - 100) / 2;
    prev_eff_load *= capacity_of(this_cpu);

    if (this_load > 0) {
        this_eff_load *= this_load +
            effective_load(tg, this_cpu, weight, weight);

        prev_eff_load *= load + effective_load(tg, prev_cpu, 0, weight);
    }

    balanced = this_eff_load <= prev_eff_load;

    schedstat_inc(p, se.statistics.nr_wakeups_affine_attempts);

    if (!balanced)
        return 0;

    schedstat_inc(sd, ttwu_move_affine);
    schedstat_inc(p, se.statistics.nr_wakeups_affine);

    return 1;
}

/*
 * find_idlest_group finds and returns the least busy CPU group within the
 * domain.
 */
static struct sched_group *
find_idlest_group(struct sched_domain *sd, struct task_struct *p,
          int this_cpu, int sd_flag)
{
    struct sched_group *idlest = NULL, *group = sd->groups;
    unsigned long min_load = ULONG_MAX, this_load = 0;
    int load_idx = sd->forkexec_idx;
    int imbalance = 100 + (sd->imbalance_pct-100)/2;

    if (sd_flag & SD_BALANCE_WAKE)
        load_idx = sd->wake_idx;

    do {
        unsigned long load, avg_load;
        int local_group;
        int i;

        /* Skip over this group if it has no CPUs allowed */
        if (!cpumask_intersects(sched_group_cpus(group),
                    tsk_cpus_allowed(p)))
            continue;

        local_group = cpumask_test_cpu(this_cpu,
                           sched_group_cpus(group));

        /* Tally up the load of all CPUs in the group */
        avg_load = 0;

        for_each_cpu(i, sched_group_cpus(group)) {
            /* Bias balancing toward cpus of our domain */
            if (local_group)
                load = source_load(i, load_idx);
            else
                load = target_load(i, load_idx);

            avg_load += load;
        }

        /* Adjust by relative CPU capacity of the group */
        avg_load = (avg_load * SCHED_CAPACITY_SCALE) / group->sgc->capacity;

        if (local_group) {
            this_load = avg_load;
        } else if (avg_load < min_load) {
            min_load = avg_load;
            idlest = group;
        }
    } while (group = group->next, group != sd->groups);

    if (!idlest || 100*this_load < imbalance*min_load)
        return NULL;
    return idlest;
}

/*
 * find_idlest_cpu - find the idlest cpu among the cpus in group.
 */
static int
find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
{
    unsigned long load, min_load = ULONG_MAX;
    unsigned int min_exit_latency = UINT_MAX;
    u64 latest_idle_timestamp = 0;
    int least_loaded_cpu = this_cpu;
    int shallowest_idle_cpu = -1;
    int i;

    /* Traverse only the allowed CPUs */
    for_each_cpu_and(i, sched_group_cpus(group), tsk_cpus_allowed(p)) {
        if (idle_cpu(i)) {
            struct rq *rq = cpu_rq(i);
            struct cpuidle_state *idle = idle_get_state(rq);
            if (idle && idle->exit_latency < min_exit_latency) {
                /*
                 * We give priority to a CPU whose idle state
                 * has the smallest exit latency irrespective
                 * of any idle timestamp.
                 */
                min_exit_latency = idle->exit_latency;
                latest_idle_timestamp = rq->idle_stamp;
                shallowest_idle_cpu = i;
            } else if ((!idle || idle->exit_latency == min_exit_latency) &&
                   rq->idle_stamp > latest_idle_timestamp) {
                /*
                 * If equal or no active idle state, then
                 * the most recently idled CPU might have
                 * a warmer cache.
                 */
                latest_idle_timestamp = rq->idle_stamp;
                shallowest_idle_cpu = i;
            }
        } else if (shallowest_idle_cpu == -1) {
            load = weighted_cpuload(i);
            if (load < min_load || (load == min_load && i == this_cpu)) {
                min_load = load;
                least_loaded_cpu = i;
            }
        }
    }

    return shallowest_idle_cpu != -1 ? shallowest_idle_cpu : least_loaded_cpu;
}

/*
 * Try and locate an idle CPU in the sched_domain.
 */
static int select_idle_sibling(struct task_struct *p, int target)
{
    struct sched_domain *sd;
    struct sched_group *sg;
    int i = task_cpu(p);

    if (idle_cpu(target))
        return target;

    /*
     * If the prevous cpu is cache affine and idle, don't be stupid.
     */
    if (i != target && cpus_share_cache(i, target) && idle_cpu(i))
        return i;

    /*
     * Otherwise, iterate the domains and find an eligible idle cpu.
     *
     * A completely idle sched group at higher domains is more
     * desirable than an idle group at a lower level, because lower
     * domains have smaller groups and usually share hardware
     * resources which causes tasks to contend on them, e.g. x86
     * hyperthread siblings in the lowest domain (SMT) can contend
     * on the shared cpu pipeline.
     *
     * However, while we prefer idle groups at higher domains
     * finding an idle cpu at the lowest domain is still better than
     * returning 'target', which we've already established, isn't
     * idle.
     */
    sd = rcu_dereference(per_cpu(sd_llc, target));
    for_each_lower_domain(sd) {
        sg = sd->groups;
        do {
            if (!cpumask_intersects(sched_group_cpus(sg),
                        tsk_cpus_allowed(p)))
                goto next;

            /* Ensure the entire group is idle */
            for_each_cpu(i, sched_group_cpus(sg)) {
                if (i == target || !idle_cpu(i))
                    goto next;
            }

            /*
             * It doesn't matter which cpu we pick, the
             * whole group is idle.
             */
            target = cpumask_first_and(sched_group_cpus(sg),
                    tsk_cpus_allowed(p));
            goto done;
next:
            sg = sg->next;
        } while (sg != sd->groups);
    }
done:
    return target;
}

/*
 * cpu_util returns the amount of capacity of a CPU that is used by CFS
 * tasks. The unit of the return value must be the one of capacity so we can
 * compare the utilization with the capacity of the CPU that is available for
 * CFS task (ie cpu_capacity).
 *
 * cfs_rq.avg.util_avg is the sum of running time of runnable tasks plus the
 * recent utilization of currently non-runnable tasks on a CPU. It represents
 * the amount of utilization of a CPU in the range [0..capacity_orig] where
 * capacity_orig is the cpu_capacity available at the highest frequency
 * (arch_scale_freq_capacity()).
 * The utilization of a CPU converges towards a sum equal to or less than the
 * current capacity (capacity_curr <= capacity_orig) of the CPU because it is
 * the running time on this CPU scaled by capacity_curr.
 *
 * Nevertheless, cfs_rq.avg.util_avg can be higher than capacity_curr or even
 * higher than capacity_orig because of unfortunate rounding in
 * cfs.avg.util_avg or just after migrating tasks and new task wakeups until
 * the average stabilizes with the new running time. We need to check that the
 * utilization stays within the range of [0..capacity_orig] and cap it if
 * necessary. Without utilization capping, a group could be seen as overloaded
 * (CPU0 utilization at 121% + CPU1 utilization at 80%) whereas CPU1 has 20% of
 * available capacity. We allow utilization to overshoot capacity_curr (but not
 * capacity_orig) as it useful for predicting the capacity required after task
 * migrations (scheduler-driven DVFS).
 */
static int cpu_util(int cpu)
{
    unsigned long util = cpu_rq(cpu)->cfs.avg.util_avg;
    unsigned long capacity = capacity_orig_of(cpu);

    return (util >= capacity) ? capacity : util;
}

/*
 * select_task_rq_fair: Select target runqueue for the waking task in domains
 * that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
 * SD_BALANCE_FORK, or SD_BALANCE_EXEC.
 *
 * Balances load by selecting the idlest cpu in the idlest group, or under
 * certain conditions an idle sibling cpu if the domain has SD_WAKE_AFFINE set.
 *
 * Returns the target cpu number.
 *
 * preempt must be disabled.
 */
static int
select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags)
{
    struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
    int cpu = smp_processor_id();
    int new_cpu = prev_cpu;
    int want_affine = 0;
    int sync = wake_flags & WF_SYNC;

    if (sd_flag & SD_BALANCE_WAKE)
        want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, tsk_cpus_allowed(p));

    rcu_read_lock();
    for_each_domain(cpu, tmp) {
        if (!(tmp->flags & SD_LOAD_BALANCE))
            break;

        /*
         * If both cpu and prev_cpu are part of this domain,
         * cpu is a valid SD_WAKE_AFFINE target.
         */
        if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
            cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
            affine_sd = tmp;
            break;
        }

        if (tmp->flags & sd_flag)
            sd = tmp;
        else if (!want_affine)
            break;
    }

    if (affine_sd) {
        sd = NULL; /* Prefer wake_affine over balance flags */
        if (cpu != prev_cpu && wake_affine(affine_sd, p, sync))
            new_cpu = cpu;
    }

    if (!sd) {
        if (sd_flag & SD_BALANCE_WAKE) /* XXX always ? */
            new_cpu = select_idle_sibling(p, new_cpu);

    } else while (sd) {
        struct sched_group *group;
        int weight;

        if (!(sd->flags & sd_flag)) {
            sd = sd->child;
            continue;
        }

        group = find_idlest_group(sd, p, cpu, sd_flag);
        if (!group) {
            sd = sd->child;
            continue;
        }

        new_cpu = find_idlest_cpu(group, p, cpu);
        if (new_cpu == -1 || new_cpu == cpu) {
            /* Now try balancing at a lower domain level of cpu */
            sd = sd->child;
            continue;
        }

        /* Now try balancing at a lower domain level of new_cpu */
        cpu = new_cpu;
        weight = sd->span_weight;
        sd = NULL;
        for_each_domain(cpu, tmp) {
            if (weight <= tmp->span_weight)
                break;
            if (tmp->flags & sd_flag)
                sd = tmp;
        }
        /* while loop will break here if sd == NULL */
    }
    rcu_read_unlock();

    return new_cpu;
}

/*
 * Called immediately before a task is migrated to a new cpu; task_cpu(p) and
 * cfs_rq_of(p) references at time of call are still valid and identify the
 * previous cpu. The caller guarantees p->pi_lock or task_rq(p)->lock is held.
 */
static void migrate_task_rq_fair(struct task_struct *p)
{
    /*
     * We are supposed to update the task to "current" time, then its up to date
     * and ready to go to new CPU/cfs_rq. But we have difficulty in getting
     * what current time is, so simply throw away the out-of-date time. This
     * will result in the wakee task is less decayed, but giving the wakee more
     * load sounds not bad.
     */
    remove_entity_load_avg(&p->se);

    /* Tell new CPU we are migrated */
    p->se.avg.last_update_time = 0;

    /* We have migrated, no longer consider this task hot */
    p->se.exec_start = 0;
}

static void task_dead_fair(struct task_struct *p)
{
    remove_entity_load_avg(&p->se);
}
#endif /* CONFIG_SMP */

static unsigned long
wakeup_gran(struct sched_entity *curr, struct sched_entity *se)
{
    /*  NICE_0_LOAD的基准最小运行期限  */
    unsigned long gran = sysctl_sched_wakeup_granularity;

    /*
     * Since its curr running now, convert the gran from real-time
     * to virtual-time in his units.
     *
     * By using 'se' instead of 'curr' we penalize light tasks, so
     * they get preempted easier. That is, if 'se' < 'curr' then
     * the resulting gran will be larger, therefore penalizing the
     * lighter, if otoh 'se' > 'curr' then the resulting gran will
     * be smaller, again penalizing the lighter task.
     *
     * This is especially important for buddies when the leftmost
     * task is higher priority than the buddy.
     *
     * 计算进程运行的期限，即抢占的粒度
     */
    return calc_delta_fair(gran, se);
}

/*
 * Should 'se' preempt 'curr'.
 *
 *         |s1
 *    |s2
 *   |s3
 *     g
 *      |<--->|c
 *
 *  w(c, s1) = -1
 *  w(c, s2) =  0
 *  w(c, s3) =  1
 *
 */
static int
wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se)
{
    /*  vdiff为curr和se vruntime的差值*/
    s64 gran, vdiff = curr->vruntime - se->vruntime;
    
    /*  cfs_rq的vruntime是单调递增的，也就是一个基准
     *  各个进程的vruntime追赶竞争cfsq的vruntime
     *  如果curr的vruntime比较小, 说明curr更加需要补偿, 
     *  即se无法抢占curr */
    if (vdiff <= 0)
        return -1;

    /*  计算curr的最小抢占期限粒度   */
    gran = wakeup_gran(curr, se);
    /*  当差值大于这个最小粒度的时候才抢占，这可以避免频繁抢占  */
    if (vdiff > gran)
        return 1;

    return 0;
}

static void set_last_buddy(struct sched_entity *se)
{
    if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE))
        return;

    for_each_sched_entity(se)
        cfs_rq_of(se)->last = se;
}

static void set_next_buddy(struct sched_entity *se)
{
    if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE))
        return;

    for_each_sched_entity(se)
        cfs_rq_of(se)->next = se;
}

static void set_skip_buddy(struct sched_entity *se)
{
    for_each_sched_entity(se)
        cfs_rq_of(se)->skip = se;
}

/*
 * Preempt the current task with a newly woken task if needed:
 */
static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
{
    struct task_struct *curr = rq->curr;
    struct sched_entity *se = &curr->se, *pse = &p->se;
    struct cfs_rq *cfs_rq = task_cfs_rq(curr);
    int scale = cfs_rq->nr_running >= sched_nr_latency;
    int next_buddy_marked = 0;

    if (unlikely(se == pse))
        return;

    /*
     * This is possible from callers such as attach_tasks(), in which we
     * unconditionally check_prempt_curr() after an enqueue (which may have
     * lead to a throttle).  This both saves work and prevents false
     * next-buddy nomination below.
     */
    if (unlikely(throttled_hierarchy(cfs_rq_of(pse))))
        return;

    if (sched_feat(NEXT_BUDDY) && scale && !(wake_flags & WF_FORK)) {
        set_next_buddy(pse);
        next_buddy_marked = 1;
    }

    /*
     * We can come here with TIF_NEED_RESCHED already set from new task
     * wake up path.
     *
     * Note: this also catches the edge-case of curr being in a throttled
     * group (e.g. via set_curr_task), since update_curr() (in the
     * enqueue of curr) will have resulted in resched being set.  This
     * prevents us from potentially nominating it as a false LAST_BUDDY
     * below.
     */
    if (test_tsk_need_resched(curr))
        return;

    /* Idle tasks are by definition preempted by non-idle tasks. */
    if (unlikely(curr->policy == SCHED_IDLE) &&
        likely(p->policy != SCHED_IDLE))
        goto preempt;

    /*
     * Batch and idle tasks do not preempt non-idle tasks (their preemption
     * is driven by the tick):
     */
    if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION))
        return;

    find_matching_se(&se, &pse);
    update_curr(cfs_rq_of(se));
    BUG_ON(!pse);
    if (wakeup_preempt_entity(se, pse) == 1) {
        /*
         * Bias pick_next to pick the sched entity that is
         * triggering this preemption.
         */
        if (!next_buddy_marked)
            set_next_buddy(pse);
        goto preempt;
    }

    return;

preempt:
    resched_curr(rq);
    /*
     * Only set the backward buddy when the current task is still
     * on the rq. This can happen when a wakeup gets interleaved
     * with schedule on the ->pre_schedule() or idle_balance()
     * point, either of which can * drop the rq lock.
     *
     * Also, during early boot the idle thread is in the fair class,
     * for obvious reasons its a bad idea to schedule back to it.
     */
    if (unlikely(!se->on_rq || curr == rq->idle))
        return;

    if (sched_feat(LAST_BUDDY) && scale && entity_is_task(se))
        set_last_buddy(se);
}

static struct task_struct *
pick_next_task_fair(struct rq *rq, struct task_struct *prev)
{
    struct cfs_rq *cfs_rq = &rq->cfs;
    struct sched_entity *se;
    struct task_struct *p;
    int new_tasks;

again:
#ifdef CONFIG_FAIR_GROUP_SCHED
    /*  如果nr_running计数器为0, 即当前队列上没有可运行进程,
     *  则需要调度idle进程 */
    if (!cfs_rq->nr_running)
        goto idle;
    /*  如果当前运行进程prev不是被fair调度的普通非实时进程  */
    if (prev->sched_class != &fair_sched_class)
        goto simple;

    /*
     * Because of the set_next_buddy() in dequeue_task_fair() it is rather
     * likely that a next task is from the same cgroup as the current.
     *
     * Therefore attempt to avoid putting and setting the entire cgroup
     * hierarchy, only change the part that actually changes.
     */

    do {
        struct sched_entity *curr = cfs_rq->curr;

        /*
         * Since we got here without doing put_prev_entity() we also
         * have to consider cfs_rq->curr. If it is still a runnable
         * entity, update_curr() will update its vruntime, otherwise
         * forget we've ever seen it.
         */
        if (curr)
        {
            /*  如果当前进程curr在队列上, 
             *  则需要更新起统计量和虚拟运行时间
             *  否则设置curr为空  */
            if (curr->on_rq)
                update_curr(cfs_rq);
            else
                curr = NULL;

            /*
             * This call to check_cfs_rq_runtime() will do the
             * throttle and dequeue its entity in the parent(s).
             * Therefore the 'simple' nr_running test will indeed
             * be correct.
             */
            if (unlikely(check_cfs_rq_runtime(cfs_rq)))
                goto simple;
        }
        /*  选择一个最优的调度实体  */
        se = pick_next_entity(cfs_rq, curr);
        cfs_rq = group_cfs_rq(se);
    } while (cfs_rq);  /*  如果被调度的进程仍属于当前组，那么选取下一个可能被调度的任务，以保证组间调度的公平性  */
    /*  获取调度实体se的进程实体信息  */
    p = task_of(se);

    /*
     * Since we haven't yet done put_prev_entity and if the selected task
     * is a different task than we started out with, try and touch the
     * least amount of cfs_rqs.
     */
    if (prev != p)
    {
        struct sched_entity *pse = &prev->se;

        while (!(cfs_rq = is_same_group(se, pse)))
        {
            int se_depth = se->depth;
            int pse_depth = pse->depth;

            if (se_depth <= pse_depth)
            {
                put_prev_entity(cfs_rq_of(pse), pse);
                pse = parent_entity(pse);
            }
            if (se_depth >= pse_depth)
            {
                set_next_entity(cfs_rq_of(se), se);
                se = parent_entity(se);
            }
        }

        put_prev_entity(cfs_rq, pse);
        set_next_entity(cfs_rq, se);
    }

    if (hrtick_enabled(rq))
        hrtick_start_fair(rq, p);

    return p;
simple:
    cfs_rq = &rq->cfs;
#endif
    /*  如果nr_running计数器为0,
     *  当前队列上没有可运行进程,
     *  则需要调度idle进程  */
    if (!cfs_rq->nr_running)
        goto idle;
    /*  将当前进程放入运行队列的合适位置  */
    put_prev_task(rq, prev);

    do
    {
        /*  选出下一个可执行调度实体(进程)  */
        se = pick_next_entity(cfs_rq, NULL);
        /*  把选中的进程从红黑树移除，更新红黑树  
         *  set_next_entity会调用__dequeue_entity完成此工作  */
        set_next_entity(cfs_rq, se);
        /*  group_cfs_rq return NULL when !CONFIG_FAIR_GROUP_SCHED
         *  在非组调度情况下, group_cfs_rq返回了NULL  */
        cfs_rq = group_cfs_rq(se);
    } while (cfs_rq);  /*  在没有配置组调度选项(CONFIG_FAIR_GROUP_SCHED)的情况下.group_cfs_rq()返回NULL.因此,上函数中的循环只会循环一次  */


    /*  获取到调度实体指代的进程信息  */
    p = task_of(se);

    if (hrtick_enabled(rq))
        hrtick_start_fair(rq, p);

    return p;

idle:
    /*
     * This is OK, because current is on_cpu, which avoids it being picked
     * for load-balance and preemption/IRQs are still disabled avoiding
     * further scheduler activity on it and we're being very careful to
     * re-start the picking loop.
     */
    lockdep_unpin_lock(&rq->lock);
    new_tasks = idle_balance(rq);
    lockdep_pin_lock(&rq->lock);
    /*
     * Because idle_balance() releases (and re-acquires) rq->lock, it is
     * possible for any higher priority task to appear. In that case we
     * must re-start the pick_next_entity() loop.
     */
    if (new_tasks < 0)
        return RETRY_TASK;

    if (new_tasks > 0)
        goto again;

    return NULL;
}

/*
 * Account for a descheduled task:
 */
static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
{
    struct sched_entity *se = &prev->se;
    struct cfs_rq *cfs_rq;

    for_each_sched_entity(se) {
        cfs_rq = cfs_rq_of(se);
        put_prev_entity(cfs_rq, se);
    }
}

/*
 * sched_yield() is very simple
 *
 * The magic of dealing with the ->skip buddy is in pick_next_entity.
 */
static void yield_task_fair(struct rq *rq)
{
    struct task_struct *curr = rq->curr;
    struct cfs_rq *cfs_rq = task_cfs_rq(curr);
    struct sched_entity *se = &curr->se;

    /*
     * Are we the only task in the tree?
     */
    if (unlikely(rq->nr_running == 1))
        return;

    clear_buddies(cfs_rq, se);

    if (curr->policy != SCHED_BATCH) {
        update_rq_clock(rq);
        /*
         * Update run-time statistics of the 'current'.
         */
        update_curr(cfs_rq);
        /*
         * Tell update_rq_clock() that we've just updated,
         * so we don't do microscopic update in schedule()
         * and double the fastpath cost.
         */
        rq_clock_skip_update(rq, true);
    }

    set_skip_buddy(se);
}

static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preempt)
{
    struct sched_entity *se = &p->se;

    /* throttled hierarchies are not runnable */
    if (!se->on_rq || throttled_hierarchy(cfs_rq_of(se)))
        return false;

    /* Tell the scheduler that we'd really like pse to run next. */
    set_next_buddy(se);

    yield_task_fair(rq);

    return true;
}

#ifdef CONFIG_SMP
/**************************************************
 * Fair scheduling class load-balancing methods.
 *
 * BASICS
 *
 * The purpose of load-balancing is to achieve the same basic fairness the
 * per-cpu scheduler provides, namely provide a proportional amount of compute
 * time to each task. This is expressed in the following equation:
 *
 *   W_i,n/P_i == W_j,n/P_j for all i,j                   (1)
 *
 * Where W_i,n is the n-th weight average for cpu i. The instantaneous weight
 * W_i,0 is defined as:
 *
 *   W_i,0 = \Sum_j w_i,j                         (2)
 *
 * Where w_i,j is the weight of the j-th runnable task on cpu i. This weight
 * is derived from the nice value as per prio_to_weight[].
 *
 * The weight average is an exponential decay average of the instantaneous
 * weight:
 *
 *   W'_i,n = (2^n - 1) / 2^n * W_i,n + 1 / 2^n * W_i,0           (3)
 *
 * C_i is the compute capacity of cpu i, typically it is the
 * fraction of 'recent' time available for SCHED_OTHER task execution. But it
 * can also include other factors [XXX].
 *
 * To achieve this balance we define a measure of imbalance which follows
 * directly from (1):
 *
 *   imb_i,j = max{ avg(W/C), W_i/C_i } - min{ avg(W/C), W_j/C_j }    (4)
 *
 * We them move tasks around to minimize the imbalance. In the continuous
 * function space it is obvious this converges, in the discrete case we get
 * a few fun cases generally called infeasible weight scenarios.
 *
 * [XXX expand on:
 *     - infeasible weights;
 *     - local vs global optima in the discrete case. ]
 *
 *
 * SCHED DOMAINS
 *
 * In order to solve the imbalance equation (4), and avoid the obvious O(n^2)
 * for all i,j solution, we create a tree of cpus that follows the hardware
 * topology where each level pairs two lower groups (or better). This results
 * in O(log n) layers. Furthermore we reduce the number of cpus going up the
 * tree to only the first of the previous level and we decrease the frequency
 * of load-balance at each level inv. proportional to the number of cpus in
 * the groups.
 *
 * This yields:
 *
 *     log_2 n     1     n
 *   \Sum       { --- * --- * 2^i } = O(n)                (5)
 *     i = 0      2^i   2^i
 *                   `- size of each group
 *     |     |     `- number of cpus doing load-balance
 *     |     `- freq
 *     `- sum over all levels
 *
 * Coupled with a limit on how many tasks we can migrate every balance pass,
 * this makes (5) the runtime complexity of the balancer.
 *
 * An important property here is that each CPU is still (indirectly) connected
 * to every other cpu in at most O(log n) steps:
 *
 * The adjacency matrix of the resulting graph is given by:
 *
 *         log_2 n     
 *   A_i,j = \Union     (i % 2^k == 0) && i / 2^(k+1) == j / 2^(k+1)  (6)
 *         k = 0
 *
 * And you'll find that:
 *
 *   A^(log_2 n)_i,j != 0  for all i,j                (7)
 *
 * Showing there's indeed a path between every cpu in at most O(log n) steps.
 * The task movement gives a factor of O(m), giving a convergence complexity
 * of:
 *
 *   O(nm log n),  n := nr_cpus, m := nr_tasks            (8)
 *
 *
 * WORK CONSERVING
 *
 * In order to avoid CPUs going idle while there's still work to do, new idle
 * balancing is more aggressive and has the newly idle cpu iterate up the domain
 * tree itself instead of relying on other CPUs to bring it work.
 *
 * This adds some complexity to both (5) and (8) but it reduces the total idle
 * time.
 *
 * [XXX more?]
 *
 *
 * CGROUPS
 *
 * Cgroups make a horror show out of (2), instead of a simple sum we get:
 *
 *                s_k,i
 *   W_i,0 = \Sum_j \Prod_k w_k * -----                   (9)
 *                 S_k
 *
 * Where
 *
 *   s_k,i = \Sum_j w_i,j,k  and  S_k = \Sum_i s_k,i         (10)
 *
 * w_i,j,k is the weight of the j-th runnable task in the k-th cgroup on cpu i.
 *
 * The big problem is S_k, its a global sum needed to compute a local (W_i)
 * property.
 *
 * [XXX write more on how we solve this.. _after_ merging pjt's patches that
 *      rewrite all of this once again.]
 */ 

static unsigned long __read_mostly max_load_balance_interval = HZ/10;

enum fbq_type { regular, remote, all };

#define LBF_ALL_PINNED  0x01
#define LBF_NEED_BREAK  0x02
#define LBF_DST_PINNED  0x04
#define LBF_SOME_PINNED 0x08

struct lb_env {
    struct sched_domain     *sd;

    struct rq           *src_rq;
    int             src_cpu;

    int             dst_cpu;
    struct rq           *dst_rq;

    struct cpumask      *dst_grpmask;
    int             new_dst_cpu;
    enum cpu_idle_type      idle;
    long            imbalance;
    /* The set of CPUs under consideration for load-balancing */
    struct cpumask      *cpus;

    unsigned int        flags;

    unsigned int        loop;
    unsigned int        loop_break;
    unsigned int        loop_max;

    enum fbq_type       fbq_type;
    struct list_head    tasks;
};

/*
 * Is this task likely cache-hot:
 */
static int task_hot(struct task_struct *p, struct lb_env *env)
{
    s64 delta;

    lockdep_assert_held(&env->src_rq->lock);

    if (p->sched_class != &fair_sched_class)
        return 0;

    if (unlikely(p->policy == SCHED_IDLE))
        return 0;

    /*
     * Buddy candidates are cache hot:
     */
    if (sched_feat(CACHE_HOT_BUDDY) && env->dst_rq->nr_running &&
            (&p->se == cfs_rq_of(&p->se)->next ||
             &p->se == cfs_rq_of(&p->se)->last))
        return 1;

    if (sysctl_sched_migration_cost == -1)
        return 1;
    if (sysctl_sched_migration_cost == 0)
        return 0;

    delta = rq_clock_task(env->src_rq) - p->se.exec_start;

    return delta < (s64)sysctl_sched_migration_cost;
}

#ifdef CONFIG_NUMA_BALANCING
/*
 * Returns 1, if task migration degrades locality
 * Returns 0, if task migration improves locality i.e migration preferred.
 * Returns -1, if task migration is not affected by locality.
 */
static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
{
    struct numa_group *numa_group = rcu_dereference(p->numa_group);
    unsigned long src_faults, dst_faults;
    int src_nid, dst_nid;

    if (!static_branch_likely(&sched_numa_balancing))
        return -1;

    if (!p->numa_faults || !(env->sd->flags & SD_NUMA))
        return -1;

    src_nid = cpu_to_node(env->src_cpu);
    dst_nid = cpu_to_node(env->dst_cpu);

    if (src_nid == dst_nid)
        return -1;

    /* Migrating away from the preferred node is always bad. */
    if (src_nid == p->numa_preferred_nid) {
        if (env->src_rq->nr_running > env->src_rq->nr_preferred_running)
            return 1;
        else
            return -1;
    }

    /* Encourage migration to the preferred node. */
    if (dst_nid == p->numa_preferred_nid)
        return 0;

    if (numa_group) {
        src_faults = group_faults(p, src_nid);
        dst_faults = group_faults(p, dst_nid);
    } else {
        src_faults = task_faults(p, src_nid);
        dst_faults = task_faults(p, dst_nid);
    }

    return dst_faults < src_faults;
}

#else
static inline int migrate_degrades_locality(struct task_struct *p,
                         struct lb_env *env)
{
    return -1;
}
#endif

/*
 * can_migrate_task - may task p from runqueue rq be migrated to this_cpu?
 */
static
int can_migrate_task(struct task_struct *p, struct lb_env *env)
{
    int tsk_cache_hot;

    lockdep_assert_held(&env->src_rq->lock);

    /*
     * We do not migrate tasks that are:
     * 1) throttled_lb_pair, or
     * 2) cannot be migrated to this CPU due to cpus_allowed, or
     * 3) running (obviously), or
     * 4) are cache-hot on their current CPU.
     */
    if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
        return 0;

    if (!cpumask_test_cpu(env->dst_cpu, tsk_cpus_allowed(p))) {
        int cpu;

        schedstat_inc(p, se.statistics.nr_failed_migrations_affine);

        env->flags |= LBF_SOME_PINNED;

        /*
         * Remember if this task can be migrated to any other cpu in
         * our sched_group. We may want to revisit it if we couldn't
         * meet load balance goals by pulling other tasks on src_cpu.
         *
         * Also avoid computing new_dst_cpu if we have already computed
         * one in current iteration.
         */
        if (!env->dst_grpmask || (env->flags & LBF_DST_PINNED))
            return 0;

        /* Prevent to re-select dst_cpu via env's cpus */
        for_each_cpu_and(cpu, env->dst_grpmask, env->cpus) {
            if (cpumask_test_cpu(cpu, tsk_cpus_allowed(p))) {
                env->flags |= LBF_DST_PINNED;
                env->new_dst_cpu = cpu;
                break;
            }
        }

        return 0;
    }

    /* Record that we found atleast one task that could run on dst_cpu */
    env->flags &= ~LBF_ALL_PINNED;

    if (task_running(env->src_rq, p)) {
        schedstat_inc(p, se.statistics.nr_failed_migrations_running);
        return 0;
    }

    /*
     * Aggressive migration if:
     * 1) destination numa is preferred
     * 2) task is cache cold, or
     * 3) too many balance attempts have failed.
     */
    tsk_cache_hot = migrate_degrades_locality(p, env);
    if (tsk_cache_hot == -1)
        tsk_cache_hot = task_hot(p, env);

    if (tsk_cache_hot <= 0 ||
        env->sd->nr_balance_failed > env->sd->cache_nice_tries) {
        if (tsk_cache_hot == 1) {
            schedstat_inc(env->sd, lb_hot_gained[env->idle]);
            schedstat_inc(p, se.statistics.nr_forced_migrations);
        }
        return 1;
    }

    schedstat_inc(p, se.statistics.nr_failed_migrations_hot);
    return 0;
}

/*
 * detach_task() -- detach the task for the migration specified in env
 */
static void detach_task(struct task_struct *p, struct lb_env *env)
{
    lockdep_assert_held(&env->src_rq->lock);

    p->on_rq = TASK_ON_RQ_MIGRATING;
    deactivate_task(env->src_rq, p, 0);
    set_task_cpu(p, env->dst_cpu);
}

/*
 * detach_one_task() -- tries to dequeue exactly one task from env->src_rq, as
 * part of active balancing operations within "domain".
 *
 * Returns a task if successful and NULL otherwise.
 */
static struct task_struct *detach_one_task(struct lb_env *env)
{
    struct task_struct *p, *n;

    lockdep_assert_held(&env->src_rq->lock);

    list_for_each_entry_safe(p, n, &env->src_rq->cfs_tasks, se.group_node) {
        if (!can_migrate_task(p, env))
            continue;

        detach_task(p, env);

        /*
         * Right now, this is only the second place where
         * lb_gained[env->idle] is updated (other is detach_tasks)
         * so we can safely collect stats here rather than
         * inside detach_tasks().
         */
        schedstat_inc(env->sd, lb_gained[env->idle]);
        return p;
    }
    return NULL;
}

static const unsigned int sched_nr_migrate_break = 32;

/*
 * detach_tasks() -- tries to detach up to imbalance weighted load from
 * busiest_rq, as part of a balancing operation within domain "sd".
 *
 * Returns number of detached tasks if successful and 0 otherwise.
 */
static int detach_tasks(struct lb_env *env)
{
    struct list_head *tasks = &env->src_rq->cfs_tasks;
    struct task_struct *p;
    unsigned long load;
    int detached = 0;

    lockdep_assert_held(&env->src_rq->lock);

    if (env->imbalance <= 0)
        return 0;

    while (!list_empty(tasks)) {
        /*
         * We don't want to steal all, otherwise we may be treated likewise,
         * which could at worst lead to a livelock crash.
         */
        if (env->idle != CPU_NOT_IDLE && env->src_rq->nr_running <= 1)
            break;

        p = list_first_entry(tasks, struct task_struct, se.group_node);

        env->loop++;
        /* We've more or less seen every task there is, call it quits */
        if (env->loop > env->loop_max)
            break;

        /* take a breather every nr_migrate tasks */
        if (env->loop > env->loop_break) {
            env->loop_break += sched_nr_migrate_break;
            env->flags |= LBF_NEED_BREAK;
            break;
        }

        if (!can_migrate_task(p, env))
            goto next;

        load = task_h_load(p);

        if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)
            goto next;

        if ((load / 2) > env->imbalance)
            goto next;

        detach_task(p, env);
        list_add(&p->se.group_node, &env->tasks);

        detached++;
        env->imbalance -= load;

#ifdef CONFIG_PREEMPT
        /*
         * NEWIDLE balancing is a source of latency, so preemptible
         * kernels will stop after the first task is detached to minimize
         * the critical section.
         */
        if (env->idle == CPU_NEWLY_IDLE)
            break;
#endif

        /*
         * We only want to steal up to the prescribed amount of
         * weighted load.
         */
        if (env->imbalance <= 0)
            break;

        continue;
next:
        list_move_tail(&p->se.group_node, tasks);
    }

    /*
     * Right now, this is one of only two places we collect this stat
     * so we can safely collect detach_one_task() stats here rather
     * than inside detach_one_task().
     */
    schedstat_add(env->sd, lb_gained[env->idle], detached);

    return detached;
}

/*
 * attach_task() -- attach the task detached by detach_task() to its new rq.
 */
static void attach_task(struct rq *rq, struct task_struct *p)
{
    lockdep_assert_held(&rq->lock);

    BUG_ON(task_rq(p) != rq);
    activate_task(rq, p, 0);
    p->on_rq = TASK_ON_RQ_QUEUED;
    check_preempt_curr(rq, p, 0);
}

/*
 * attach_one_task() -- attaches the task returned from detach_one_task() to
 * its new rq.
 */
static void attach_one_task(struct rq *rq, struct task_struct *p)
{
    raw_spin_lock(&rq->lock);
    attach_task(rq, p);
    raw_spin_unlock(&rq->lock);
}

/*
 * attach_tasks() -- attaches all tasks detached by detach_tasks() to their
 * new rq.
 */
static void attach_tasks(struct lb_env *env)
{
    struct list_head *tasks = &env->tasks;
    struct task_struct *p;

    raw_spin_lock(&env->dst_rq->lock);

    while (!list_empty(tasks)) {
        p = list_first_entry(tasks, struct task_struct, se.group_node);
        list_del_init(&p->se.group_node);

        attach_task(env->dst_rq, p);
    }

    raw_spin_unlock(&env->dst_rq->lock);
}

#ifdef CONFIG_FAIR_GROUP_SCHED
static void update_blocked_averages(int cpu)
{
    struct rq *rq = cpu_rq(cpu);
    struct cfs_rq *cfs_rq;
    unsigned long flags;

    raw_spin_lock_irqsave(&rq->lock, flags);
    update_rq_clock(rq);

    /*
     * Iterates the task_group tree in a bottom up fashion, see
     * list_add_leaf_cfs_rq() for details.
     */
    for_each_leaf_cfs_rq(rq, cfs_rq) {
        /* throttled entities do not contribute to load */
        if (throttled_hierarchy(cfs_rq))
            continue;

        if (update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq))
            update_tg_load_avg(cfs_rq, 0);
    }
    raw_spin_unlock_irqrestore(&rq->lock, flags);
}

/*
 * Compute the hierarchical load factor for cfs_rq and all its ascendants.
 * This needs to be done in a top-down fashion because the load of a child
 * group is a fraction of its parents load.
 */
static void update_cfs_rq_h_load(struct cfs_rq *cfs_rq)
{
    struct rq *rq = rq_of(cfs_rq);
    struct sched_entity *se = cfs_rq->tg->se[cpu_of(rq)];
    unsigned long now = jiffies;
    unsigned long load;

    if (cfs_rq->last_h_load_update == now)
        return;

    cfs_rq->h_load_next = NULL;
    for_each_sched_entity(se) {
        cfs_rq = cfs_rq_of(se);
        cfs_rq->h_load_next = se;
        if (cfs_rq->last_h_load_update == now)
            break;
    }

    if (!se) {
        cfs_rq->h_load = cfs_rq_load_avg(cfs_rq);
        cfs_rq->last_h_load_update = now;
    }

    while ((se = cfs_rq->h_load_next) != NULL) {
        load = cfs_rq->h_load;
        load = div64_ul(load * se->avg.load_avg,
            cfs_rq_load_avg(cfs_rq) + 1);
        cfs_rq = group_cfs_rq(se);
        cfs_rq->h_load = load;
        cfs_rq->last_h_load_update = now;
    }
}

static unsigned long task_h_load(struct task_struct *p)
{
    struct cfs_rq *cfs_rq = task_cfs_rq(p);

    update_cfs_rq_h_load(cfs_rq);
    return div64_ul(p->se.avg.load_avg * cfs_rq->h_load,
            cfs_rq_load_avg(cfs_rq) + 1);
}
#else
static inline void update_blocked_averages(int cpu)
{
    struct rq *rq = cpu_rq(cpu);
    struct cfs_rq *cfs_rq = &rq->cfs;
    unsigned long flags;

    raw_spin_lock_irqsave(&rq->lock, flags);
    update_rq_clock(rq);
    update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq);
    raw_spin_unlock_irqrestore(&rq->lock, flags);
}

static unsigned long task_h_load(struct task_struct *p)
{
    return p->se.avg.load_avg;
}
#endif

/********** Helpers for find_busiest_group ************************/

enum group_type {
    group_other = 0,
    group_imbalanced,
    group_overloaded,
};

/*
 * sg_lb_stats - stats of a sched_group required for load_balancing
 */
struct sg_lb_stats {
    unsigned long avg_load; /*Avg load across the CPUs of the group */
    unsigned long group_load; /* Total load over the CPUs of the group */
    unsigned long sum_weighted_load; /* Weighted load of group's tasks */
    unsigned long load_per_task;
    unsigned long group_capacity;
    unsigned long group_util; /* Total utilization of the group */
    unsigned int sum_nr_running; /* Nr tasks running in the group */
    unsigned int idle_cpus;
    unsigned int group_weight;
    enum group_type group_type;
    int group_no_capacity;
#ifdef CONFIG_NUMA_BALANCING
    unsigned int nr_numa_running;
    unsigned int nr_preferred_running;
#endif
};

/*
 * sd_lb_stats - Structure to store the statistics of a sched_domain
 *           during load balancing.
 */
struct sd_lb_stats {
    struct sched_group *busiest;    /* Busiest group in this sd */
    struct sched_group *local;      /* Local group in this sd */
    unsigned long total_load;       /* Total load of all groups in sd */
    unsigned long total_capacity;   /* Total capacity of all groups in sd */
    unsigned long avg_load; /* Average load across all groups in sd */

    struct sg_lb_stats busiest_stat;/* Statistics of the busiest group */
    struct sg_lb_stats local_stat;  /* Statistics of the local group */
};

static inline void init_sd_lb_stats(struct sd_lb_stats *sds)
{
    /*
     * Skimp on the clearing to avoid duplicate work. We can avoid clearing
     * local_stat because update_sg_lb_stats() does a full clear/assignment.
     * We must however clear busiest_stat::avg_load because
     * update_sd_pick_busiest() reads this before assignment.
     */
    *sds = (struct sd_lb_stats){
        .busiest = NULL,
        .local = NULL,
        .total_load = 0UL,
        .total_capacity = 0UL,
        .busiest_stat = {
            .avg_load = 0UL,
            .sum_nr_running = 0,
            .group_type = group_other,
        },
    };
}

/**
 * get_sd_load_idx - Obtain the load index for a given sched domain.
 * @sd: The sched_domain whose load_idx is to be obtained.
 * @idle: The idle status of the CPU for whose sd load_idx is obtained.
 *
 * Return: The load index.
 */
static inline int get_sd_load_idx(struct sched_domain *sd,
                    enum cpu_idle_type idle)
{
    int load_idx;

    switch (idle) {
    case CPU_NOT_IDLE:
        load_idx = sd->busy_idx;
        break;

    case CPU_NEWLY_IDLE:
        load_idx = sd->newidle_idx;
        break;
    default:
        load_idx = sd->idle_idx;
        break;
    }

    return load_idx;
}

static unsigned long scale_rt_capacity(int cpu)
{
    struct rq *rq = cpu_rq(cpu);
    u64 total, used, age_stamp, avg;
    s64 delta;

    /*
     * Since we're reading these variables without serialization make sure
     * we read them once before doing sanity checks on them.
     */
    age_stamp = READ_ONCE(rq->age_stamp);
    avg = READ_ONCE(rq->rt_avg);
    delta = __rq_clock_broken(rq) - age_stamp;

    if (unlikely(delta < 0))
        delta = 0;

    total = sched_avg_period() + delta;

    used = div_u64(avg, total);

    if (likely(used < SCHED_CAPACITY_SCALE))
        return SCHED_CAPACITY_SCALE - used;

    return 1;
}

static void update_cpu_capacity(struct sched_domain *sd, int cpu)
{
    unsigned long capacity = arch_scale_cpu_capacity(sd, cpu);
    struct sched_group *sdg = sd->groups;

    cpu_rq(cpu)->cpu_capacity_orig = capacity;

    capacity *= scale_rt_capacity(cpu);
    capacity >>= SCHED_CAPACITY_SHIFT;

    if (!capacity)
        capacity = 1;

    cpu_rq(cpu)->cpu_capacity = capacity;
    sdg->sgc->capacity = capacity;
}

void update_group_capacity(struct sched_domain *sd, int cpu)
{
    struct sched_domain *child = sd->child;
    struct sched_group *group, *sdg = sd->groups;
    unsigned long capacity;
    unsigned long interval;

    interval = msecs_to_jiffies(sd->balance_interval);
    interval = clamp(interval, 1UL, max_load_balance_interval);
    sdg->sgc->next_update = jiffies + interval;

    if (!child) {
        update_cpu_capacity(sd, cpu);
        return;
    }

    capacity = 0;

    if (child->flags & SD_OVERLAP) {
        /*
         * SD_OVERLAP domains cannot assume that child groups
         * span the current group.
         */

        for_each_cpu(cpu, sched_group_cpus(sdg)) {
            struct sched_group_capacity *sgc;
            struct rq *rq = cpu_rq(cpu);

            /*
             * build_sched_domains() -> init_sched_groups_capacity()
             * gets here before we've attached the domains to the
             * runqueues.
             *
             * Use capacity_of(), which is set irrespective of domains
             * in update_cpu_capacity().
             *
             * This avoids capacity from being 0 and
             * causing divide-by-zero issues on boot.
             */
            if (unlikely(!rq->sd)) {
                capacity += capacity_of(cpu);
                continue;
            }

            sgc = rq->sd->groups->sgc;
            capacity += sgc->capacity;
        }
    } else  {
        /*
         * !SD_OVERLAP domains can assume that child groups
         * span the current group.
         */ 

        group = child->groups;
        do {
            capacity += group->sgc->capacity;
            group = group->next;
        } while (group != child->groups);
    }

    sdg->sgc->capacity = capacity;
}

/*
 * Check whether the capacity of the rq has been noticeably reduced by side
 * activity. The imbalance_pct is used for the threshold.
 * Return true is the capacity is reduced
 */
static inline int
check_cpu_capacity(struct rq *rq, struct sched_domain *sd)
{
    return ((rq->cpu_capacity * sd->imbalance_pct) <
                (rq->cpu_capacity_orig * 100));
}

/*
 * Group imbalance indicates (and tries to solve) the problem where balancing
 * groups is inadequate due to tsk_cpus_allowed() constraints.
 *
 * Imagine a situation of two groups of 4 cpus each and 4 tasks each with a
 * cpumask covering 1 cpu of the first group and 3 cpus of the second group.
 * Something like:
 *
 *      { 0 1 2 3 } { 4 5 6 7 }
 *          *     * * *
 *
 * If we were to balance group-wise we'd place two tasks in the first group and
 * two tasks in the second group. Clearly this is undesired as it will overload
 * cpu 3 and leave one of the cpus in the second group unused.
 *
 * The current solution to this issue is detecting the skew in the first group
 * by noticing the lower domain failed to reach balance and had difficulty
 * moving tasks due to affinity constraints.
 *
 * When this is so detected; this group becomes a candidate for busiest; see
 * update_sd_pick_busiest(). And calculate_imbalance() and
 * find_busiest_group() avoid some of the usual balance conditions to allow it
 * to create an effective group imbalance.
 *
 * This is a somewhat tricky proposition since the next run might not find the
 * group imbalance and decide the groups need to be balanced again. A most
 * subtle and fragile situation.
 */

static inline int sg_imbalanced(struct sched_group *group)
{
    return group->sgc->imbalance;
}

/*
 * group_has_capacity returns true if the group has spare capacity that could
 * be used by some tasks.
 * We consider that a group has spare capacity if the  * number of task is
 * smaller than the number of CPUs or if the utilization is lower than the
 * available capacity for CFS tasks.
 * For the latter, we use a threshold to stabilize the state, to take into
 * account the variance of the tasks' load and to return true if the available
 * capacity in meaningful for the load balancer.
 * As an example, an available capacity of 1% can appear but it doesn't make
 * any benefit for the load balance.
 */
static inline bool
group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs)
{
    if (sgs->sum_nr_running < sgs->group_weight)
        return true;

    if ((sgs->group_capacity * 100) >
            (sgs->group_util * env->sd->imbalance_pct))
        return true;

    return false;
}

/*
 *  group_is_overloaded returns true if the group has more tasks than it can
 *  handle.
 *  group_is_overloaded is not equals to !group_has_capacity because a group
 *  with the exact right number of tasks, has no more spare capacity but is not
 *  overloaded so both group_has_capacity and group_is_overloaded return
 *  false.
 */
static inline bool
group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs)
{
    if (sgs->sum_nr_running <= sgs->group_weight)
        return false;

    if ((sgs->group_capacity * 100) <
            (sgs->group_util * env->sd->imbalance_pct))
        return true;

    return false;
}

static inline enum
group_type group_classify(struct sched_group *group,
              struct sg_lb_stats *sgs)
{
    if (sgs->group_no_capacity)
        return group_overloaded;

    if (sg_imbalanced(group))
        return group_imbalanced;

    return group_other;
}

/**
 * update_sg_lb_stats - Update sched_group's statistics for load balancing.
 * @env: The load balancing environment.
 * @group: sched_group whose statistics are to be updated.
 * @load_idx: Load index of sched_domain of this_cpu for load calc.
 * @local_group: Does group contain this_cpu.
 * @sgs: variable to hold the statistics for this group.
 * @overload: Indicate more than one runnable task for any CPU.
 */
static inline void update_sg_lb_stats(struct lb_env *env,
            struct sched_group *group, int load_idx,
            int local_group, struct sg_lb_stats *sgs,
            bool *overload)
{
    unsigned long load;
    int i, nr_running;

    memset(sgs, 0, sizeof(*sgs));

    for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
        struct rq *rq = cpu_rq(i);

        /* Bias balancing toward cpus of our domain */
        if (local_group)
            load = target_load(i, load_idx);
        else
            load = source_load(i, load_idx);

        sgs->group_load += load;
        sgs->group_util += cpu_util(i);
        sgs->sum_nr_running += rq->cfs.h_nr_running;

        nr_running = rq->nr_running;
        if (nr_running > 1)
            *overload = true;

#ifdef CONFIG_NUMA_BALANCING
        sgs->nr_numa_running += rq->nr_numa_running;
        sgs->nr_preferred_running += rq->nr_preferred_running;
#endif
        sgs->sum_weighted_load += weighted_cpuload(i);
        /*
         * No need to call idle_cpu() if nr_running is not 0
         */
        if (!nr_running && idle_cpu(i))
            sgs->idle_cpus++;
    }

    /* Adjust by relative CPU capacity of the group */
    sgs->group_capacity = group->sgc->capacity;
    sgs->avg_load = (sgs->group_load*SCHED_CAPACITY_SCALE) / sgs->group_capacity;

    if (sgs->sum_nr_running)
        sgs->load_per_task = sgs->sum_weighted_load / sgs->sum_nr_running;

    sgs->group_weight = group->group_weight;

    sgs->group_no_capacity = group_is_overloaded(env, sgs);
    sgs->group_type = group_classify(group, sgs);
}

/**
 * update_sd_pick_busiest - return 1 on busiest group
 * @env: The load balancing environment.
 * @sds: sched_domain statistics
 * @sg: sched_group candidate to be checked for being the busiest
 * @sgs: sched_group statistics
 *
 * Determine if @sg is a busier group than the previously selected
 * busiest group.
 *
 * Return: %true if @sg is a busier group than the previously selected
 * busiest group. %false otherwise.
 */
static bool update_sd_pick_busiest(struct lb_env *env,
                   struct sd_lb_stats *sds,
                   struct sched_group *sg,
                   struct sg_lb_stats *sgs)
{
    struct sg_lb_stats *busiest = &sds->busiest_stat;

    if (sgs->group_type > busiest->group_type)
        return true;

    if (sgs->group_type < busiest->group_type)
        return false;

    if (sgs->avg_load <= busiest->avg_load)
        return false;

    /* This is the busiest node in its class. */
    if (!(env->sd->flags & SD_ASYM_PACKING))
        return true;

    /*
     * ASYM_PACKING needs to move all the work to the lowest
     * numbered CPUs in the group, therefore mark all groups
     * higher than ourself as busy.
     */
    if (sgs->sum_nr_running && env->dst_cpu < group_first_cpu(sg)) {
        if (!sds->busiest)
            return true;

        if (group_first_cpu(sds->busiest) > group_first_cpu(sg))
            return true;
    }

    return false;
}

#ifdef CONFIG_NUMA_BALANCING
static inline enum fbq_type fbq_classify_group(struct sg_lb_stats *sgs)
{
    if (sgs->sum_nr_running > sgs->nr_numa_running)
        return regular;
    if (sgs->sum_nr_running > sgs->nr_preferred_running)
        return remote;
    return all;
}

static inline enum fbq_type fbq_classify_rq(struct rq *rq)
{
    if (rq->nr_running > rq->nr_numa_running)
        return regular;
    if (rq->nr_running > rq->nr_preferred_running)
        return remote;
    return all;
}
#else
static inline enum fbq_type fbq_classify_group(struct sg_lb_stats *sgs)
{
    return all;
}

static inline enum fbq_type fbq_classify_rq(struct rq *rq)
{
    return regular;
}
#endif /* CONFIG_NUMA_BALANCING */

/**
 * update_sd_lb_stats - Update sched_domain's statistics for load balancing.
 * @env: The load balancing environment.
 * @sds: variable to hold the statistics for this sched_domain.
 */
static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sds)
{
    struct sched_domain *child = env->sd->child;
    struct sched_group *sg = env->sd->groups;
    struct sg_lb_stats tmp_sgs;
    int load_idx, prefer_sibling = 0;
    bool overload = false;

    if (child && child->flags & SD_PREFER_SIBLING)
        prefer_sibling = 1;

    load_idx = get_sd_load_idx(env->sd, env->idle);

    do {
        struct sg_lb_stats *sgs = &tmp_sgs;
        int local_group;

        local_group = cpumask_test_cpu(env->dst_cpu, sched_group_cpus(sg));
        if (local_group) {
            sds->local = sg;
            sgs = &sds->local_stat;

            if (env->idle != CPU_NEWLY_IDLE ||
                time_after_eq(jiffies, sg->sgc->next_update))
                update_group_capacity(env->sd, env->dst_cpu);
        }

        update_sg_lb_stats(env, sg, load_idx, local_group, sgs,
                        &overload);

        if (local_group)
            goto next_group;

        /*
         * In case the child domain prefers tasks go to siblings
         * first, lower the sg capacity so that we'll try
         * and move all the excess tasks away. We lower the capacity
         * of a group only if the local group has the capacity to fit
         * these excess tasks. The extra check prevents the case where
         * you always pull from the heaviest group when it is already
         * under-utilized (possible with a large weight task outweighs
         * the tasks on the system).
         */
        if (prefer_sibling && sds->local &&
            group_has_capacity(env, &sds->local_stat) &&
            (sgs->sum_nr_running > 1)) {
            sgs->group_no_capacity = 1;
            sgs->group_type = group_classify(sg, sgs);
        }

        if (update_sd_pick_busiest(env, sds, sg, sgs)) {
            sds->busiest = sg;
            sds->busiest_stat = *sgs;
        }

next_group:
        /* Now, start updating sd_lb_stats */
        sds->total_load += sgs->group_load;
        sds->total_capacity += sgs->group_capacity;

        sg = sg->next;
    } while (sg != env->sd->groups);

    if (env->sd->flags & SD_NUMA)
        env->fbq_type = fbq_classify_group(&sds->busiest_stat);

    if (!env->sd->parent) {
        /* update overload indicator if we are at root domain */
        if (env->dst_rq->rd->overload != overload)
            env->dst_rq->rd->overload = overload;
    }

}

/**
 * check_asym_packing - Check to see if the group is packed into the
 *              sched doman.
 *
 * This is primarily intended to used at the sibling level.  Some
 * cores like POWER7 prefer to use lower numbered SMT threads.  In the
 * case of POWER7, it can move to lower SMT modes only when higher
 * threads are idle.  When in lower SMT modes, the threads will
 * perform better since they share less core resources.  Hence when we
 * have idle threads, we want them to be the higher ones.
 *
 * This packing function is run on idle threads.  It checks to see if
 * the busiest CPU in this domain (core in the P7 case) has a higher
 * CPU number than the packing function is being run on.  Here we are
 * assuming lower CPU number will be equivalent to lower a SMT thread
 * number.
 *
 * Return: 1 when packing is required and a task should be moved to
 * this CPU.  The amount of the imbalance is returned in *imbalance.
 *
 * @env: The load balancing environment.
 * @sds: Statistics of the sched_domain which is to be packed
 */
static int check_asym_packing(struct lb_env *env, struct sd_lb_stats *sds)
{
    int busiest_cpu;

    if (!(env->sd->flags & SD_ASYM_PACKING))
        return 0;

    if (!sds->busiest)
        return 0;

    busiest_cpu = group_first_cpu(sds->busiest);
    if (env->dst_cpu > busiest_cpu)
        return 0;

    env->imbalance = DIV_ROUND_CLOSEST(
        sds->busiest_stat.avg_load * sds->busiest_stat.group_capacity,
        SCHED_CAPACITY_SCALE);

    return 1;
}

/**
 * fix_small_imbalance - Calculate the minor imbalance that exists
 *              amongst the groups of a sched_domain, during
 *              load balancing.
 * @env: The load balancing environment.
 * @sds: Statistics of the sched_domain whose imbalance is to be calculated.
 */
static inline
void fix_small_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
{
    unsigned long tmp, capa_now = 0, capa_move = 0;
    unsigned int imbn = 2;
    unsigned long scaled_busy_load_per_task;
    struct sg_lb_stats *local, *busiest;

    local = &sds->local_stat;
    busiest = &sds->busiest_stat;

    if (!local->sum_nr_running)
        local->load_per_task = cpu_avg_load_per_task(env->dst_cpu);
    else if (busiest->load_per_task > local->load_per_task)
        imbn = 1;

    scaled_busy_load_per_task =
        (busiest->load_per_task * SCHED_CAPACITY_SCALE) /
        busiest->group_capacity;

    if (busiest->avg_load + scaled_busy_load_per_task >=
        local->avg_load + (scaled_busy_load_per_task * imbn)) {
        env->imbalance = busiest->load_per_task;
        return;
    }

    /*
     * OK, we don't have enough imbalance to justify moving tasks,
     * however we may be able to increase total CPU capacity used by
     * moving them.
     */

    capa_now += busiest->group_capacity *
            min(busiest->load_per_task, busiest->avg_load);
    capa_now += local->group_capacity *
            min(local->load_per_task, local->avg_load);
    capa_now /= SCHED_CAPACITY_SCALE;

    /* Amount of load we'd subtract */
    if (busiest->avg_load > scaled_busy_load_per_task) {
        capa_move += busiest->group_capacity *
                min(busiest->load_per_task,
                busiest->avg_load - scaled_busy_load_per_task);
    }

    /* Amount of load we'd add */
    if (busiest->avg_load * busiest->group_capacity <
        busiest->load_per_task * SCHED_CAPACITY_SCALE) {
        tmp = (busiest->avg_load * busiest->group_capacity) /
              local->group_capacity;
    } else {
        tmp = (busiest->load_per_task * SCHED_CAPACITY_SCALE) /
              local->group_capacity;
    }
    capa_move += local->group_capacity *
            min(local->load_per_task, local->avg_load + tmp);
    capa_move /= SCHED_CAPACITY_SCALE;

    /* Move if we gain throughput */
    if (capa_move > capa_now)
        env->imbalance = busiest->load_per_task;
}

/**
 * calculate_imbalance - Calculate the amount of imbalance present within the
 *               groups of a given sched_domain during load balance.
 * @env: load balance environment
 * @sds: statistics of the sched_domain whose imbalance is to be calculated.
 */
static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
{
    unsigned long max_pull, load_above_capacity = ~0UL;
    struct sg_lb_stats *local, *busiest;

    local = &sds->local_stat;
    busiest = &sds->busiest_stat;

    if (busiest->group_type == group_imbalanced) {
        /*
         * In the group_imb case we cannot rely on group-wide averages
         * to ensure cpu-load equilibrium, look at wider averages. XXX
         */
        busiest->load_per_task =
            min(busiest->load_per_task, sds->avg_load);
    }

    /*
     * In the presence of smp nice balancing, certain scenarios can have
     * max load less than avg load(as we skip the groups at or below
     * its cpu_capacity, while calculating max_load..)
     */
    if (busiest->avg_load <= sds->avg_load ||
        local->avg_load >= sds->avg_load) {
        env->imbalance = 0;
        return fix_small_imbalance(env, sds);
    }

    /*
     * If there aren't any idle cpus, avoid creating some.
     */
    if (busiest->group_type == group_overloaded &&
        local->group_type   == group_overloaded) {
        load_above_capacity = busiest->sum_nr_running *
                    SCHED_LOAD_SCALE;
        if (load_above_capacity > busiest->group_capacity)
            load_above_capacity -= busiest->group_capacity;
        else
            load_above_capacity = ~0UL;
    }

    /*
     * We're trying to get all the cpus to the average_load, so we don't
     * want to push ourselves above the average load, nor do we wish to
     * reduce the max loaded cpu below the average load. At the same time,
     * we also don't want to reduce the group load below the group capacity
     * (so that we can implement power-savings policies etc). Thus we look
     * for the minimum possible imbalance.
     */
    max_pull = min(busiest->avg_load - sds->avg_load, load_above_capacity);

    /* How much load to actually move to equalise the imbalance */
    env->imbalance = min(
        max_pull * busiest->group_capacity,
        (sds->avg_load - local->avg_load) * local->group_capacity
    ) / SCHED_CAPACITY_SCALE;

    /*
     * if *imbalance is less than the average load per runnable task
     * there is no guarantee that any tasks will be moved so we'll have
     * a think about bumping its value to force at least one task to be
     * moved
     */
    if (env->imbalance < busiest->load_per_task)
        return fix_small_imbalance(env, sds);
}

/******* find_busiest_group() helpers end here *********************/

/**
 * find_busiest_group - Returns the busiest group within the sched_domain
 * if there is an imbalance. If there isn't an imbalance, and
 * the user has opted for power-savings, it returns a group whose
 * CPUs can be put to idle by rebalancing those tasks elsewhere, if
 * such a group exists.
 *
 * Also calculates the amount of weighted load which should be moved
 * to restore balance.
 *
 * @env: The load balancing environment.
 *
 * Return:      - The busiest group if imbalance exists.
 *          - If no imbalance and user has opted for power-savings balance,
 *         return the least loaded group whose CPUs can be
 *         put to idle by rebalancing its tasks onto our group.
 */
static struct sched_group *find_busiest_group(struct lb_env *env)
{
    struct sg_lb_stats *local, *busiest;
    struct sd_lb_stats sds;

    init_sd_lb_stats(&sds);

    /*
     * Compute the various statistics relavent for load balancing at
     * this level.
     */
    update_sd_lb_stats(env, &sds);
    local = &sds.local_stat;
    busiest = &sds.busiest_stat;

    /* ASYM feature bypasses nice load balance check */
    if ((env->idle == CPU_IDLE || env->idle == CPU_NEWLY_IDLE) &&
        check_asym_packing(env, &sds))
        return sds.busiest;

    /* There is no busy sibling group to pull tasks from */
    if (!sds.busiest || busiest->sum_nr_running == 0)
        goto out_balanced;

    sds.avg_load = (SCHED_CAPACITY_SCALE * sds.total_load)
                        / sds.total_capacity;

    /*
     * If the busiest group is imbalanced the below checks don't
     * work because they assume all things are equal, which typically
     * isn't true due to cpus_allowed constraints and the like.
     */
    if (busiest->group_type == group_imbalanced)
        goto force_balance;

    /* SD_BALANCE_NEWIDLE trumps SMP nice when underutilized */
    if (env->idle == CPU_NEWLY_IDLE && group_has_capacity(env, local) &&
        busiest->group_no_capacity)
        goto force_balance;

    /*
     * If the local group is busier than the selected busiest group
     * don't try and pull any tasks.
     */
    if (local->avg_load >= busiest->avg_load)
        goto out_balanced;

    /*
     * Don't pull any tasks if this group is already above the domain
     * average load.
     */
    if (local->avg_load >= sds.avg_load)
        goto out_balanced;

    if (env->idle == CPU_IDLE) {
        /*
         * This cpu is idle. If the busiest group is not overloaded
         * and there is no imbalance between this and busiest group
         * wrt idle cpus, it is balanced. The imbalance becomes
         * significant if the diff is greater than 1 otherwise we
         * might end up to just move the imbalance on another group
         */
        if ((busiest->group_type != group_overloaded) &&
                (local->idle_cpus <= (busiest->idle_cpus + 1)))
            goto out_balanced;
    } else {
        /*
         * In the CPU_NEWLY_IDLE, CPU_NOT_IDLE cases, use
         * imbalance_pct to be conservative.
         */
        if (100 * busiest->avg_load <=
                env->sd->imbalance_pct * local->avg_load)
            goto out_balanced;
    }

force_balance:
    /* Looks like there is an imbalance. Compute it */
    calculate_imbalance(env, &sds);
    return sds.busiest;

out_balanced:
    env->imbalance = 0;
    return NULL;
}

/*
 * find_busiest_queue - find the busiest runqueue among the cpus in group.
 */
static struct rq *find_busiest_queue(struct lb_env *env,
                     struct sched_group *group)
{
    struct rq *busiest = NULL, *rq;
    unsigned long busiest_load = 0, busiest_capacity = 1;
    int i;

    for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
        unsigned long capacity, wl;
        enum fbq_type rt;

        rq = cpu_rq(i);
        rt = fbq_classify_rq(rq);

        /*
         * We classify groups/runqueues into three groups:
         *  - regular: there are !numa tasks
         *  - remote:  there are numa tasks that run on the 'wrong' node
         *  - all:     there is no distinction
         *
         * In order to avoid migrating ideally placed numa tasks,
         * ignore those when there's better options.
         *
         * If we ignore the actual busiest queue to migrate another
         * task, the next balance pass can still reduce the busiest
         * queue by moving tasks around inside the node.
         *
         * If we cannot move enough load due to this classification
         * the next pass will adjust the group classification and
         * allow migration of more tasks.
         *
         * Both cases only affect the total convergence complexity.
         */
        if (rt > env->fbq_type)
            continue;

        capacity = capacity_of(i);

        wl = weighted_cpuload(i);

        /*
         * When comparing with imbalance, use weighted_cpuload()
         * which is not scaled with the cpu capacity.
         */

        if (rq->nr_running == 1 && wl > env->imbalance &&
            !check_cpu_capacity(rq, env->sd))
            continue;

        /*
         * For the load comparisons with the other cpu's, consider
         * the weighted_cpuload() scaled with the cpu capacity, so
         * that the load can be moved away from the cpu that is
         * potentially running at a lower capacity.
         *
         * Thus we're looking for max(wl_i / capacity_i), crosswise
         * multiplication to rid ourselves of the division works out
         * to: wl_i * capacity_j > wl_j * capacity_i;  where j is
         * our previous maximum.
         */
        if (wl * busiest_capacity > busiest_load * capacity) {
            busiest_load = wl;
            busiest_capacity = capacity;
            busiest = rq;
        }
    }

    return busiest;
}

/*
 * Max backoff if we encounter pinned tasks. Pretty arbitrary value, but
 * so long as it is large enough.
 */
#define MAX_PINNED_INTERVAL     512

/* Working cpumask for load_balance and load_balance_newidle. */
DEFINE_PER_CPU(cpumask_var_t, load_balance_mask);

static int need_active_balance(struct lb_env *env)
{
    struct sched_domain *sd = env->sd;

    if (env->idle == CPU_NEWLY_IDLE) {

        /*
         * ASYM_PACKING needs to force migrate tasks from busy but
         * higher numbered CPUs in order to pack all tasks in the
         * lowest numbered CPUs.
         */
        if ((sd->flags & SD_ASYM_PACKING) && env->src_cpu > env->dst_cpu)
            return 1;
    }

    /*
     * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.
     * It's worth migrating the task if the src_cpu's capacity is reduced
     * because of other sched_class or IRQs if more capacity stays
     * available on dst_cpu.
     */
    if ((env->idle != CPU_NOT_IDLE) &&
        (env->src_rq->cfs.h_nr_running == 1)) {
        if ((check_cpu_capacity(env->src_rq, sd)) &&
            (capacity_of(env->src_cpu)*sd->imbalance_pct < capacity_of(env->dst_cpu)*100))
            return 1;
    }

    return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2);
}

static int active_load_balance_cpu_stop(void *data);

static int should_we_balance(struct lb_env *env)
{
    struct sched_group *sg = env->sd->groups;
    struct cpumask *sg_cpus, *sg_mask;
    int cpu, balance_cpu = -1;

    /*
     * In the newly idle case, we will allow all the cpu's
     * to do the newly idle load balance.
     */
    if (env->idle == CPU_NEWLY_IDLE)
        return 1;

    sg_cpus = sched_group_cpus(sg);
    sg_mask = sched_group_mask(sg);
    /* Try to find first idle cpu */
    for_each_cpu_and(cpu, sg_cpus, env->cpus) {
        if (!cpumask_test_cpu(cpu, sg_mask) || !idle_cpu(cpu))
            continue;

        balance_cpu = cpu;
        break;
    }

    if (balance_cpu == -1)
        balance_cpu = group_balance_cpu(sg);

    /*
     * First idle cpu or the first cpu(busiest) in this sched group
     * is eligible for doing load balancing at this and above domains.
     */
    return balance_cpu == env->dst_cpu;
}

/*
 * Check this_cpu to ensure it is balanced within domain. Attempt to move
 * tasks if there is an imbalance.
 */
static int load_balance(int this_cpu, struct rq *this_rq,
            struct sched_domain *sd, enum cpu_idle_type idle,
            int *continue_balancing)
{
    int ld_moved, cur_ld_moved, active_balance = 0;
    struct sched_domain *sd_parent = sd->parent;
    struct sched_group *group;
    struct rq *busiest;
    unsigned long flags;
    struct cpumask *cpus = this_cpu_cpumask_var_ptr(load_balance_mask);

    struct lb_env env = {
        .sd         = sd,
        .dst_cpu    = this_cpu,
        .dst_rq     = this_rq,
        .dst_grpmask    = sched_group_cpus(sd->groups),
        .idle       = idle,
        .loop_break     = sched_nr_migrate_break,
        .cpus       = cpus,
        .fbq_type       = all,
        .tasks      = LIST_HEAD_INIT(env.tasks),
    };

    /*
     * For NEWLY_IDLE load_balancing, we don't need to consider
     * other cpus in our group
     */
    if (idle == CPU_NEWLY_IDLE)
        env.dst_grpmask = NULL;

    cpumask_copy(cpus, cpu_active_mask);

    schedstat_inc(sd, lb_count[idle]);

redo:
    if (!should_we_balance(&env)) {
        *continue_balancing = 0;
        goto out_balanced;
    }

    group = find_busiest_group(&env);
    if (!group) {
        schedstat_inc(sd, lb_nobusyg[idle]);
        goto out_balanced;
    }

    busiest = find_busiest_queue(&env, group);
    if (!busiest) {
        schedstat_inc(sd, lb_nobusyq[idle]);
        goto out_balanced;
    }

    BUG_ON(busiest == env.dst_rq);

    schedstat_add(sd, lb_imbalance[idle], env.imbalance);

    env.src_cpu = busiest->cpu;
    env.src_rq = busiest;

    ld_moved = 0;
    if (busiest->nr_running > 1) {
        /*
         * Attempt to move tasks. If find_busiest_group has found
         * an imbalance but busiest->nr_running <= 1, the group is
         * still unbalanced. ld_moved simply stays zero, so it is
         * correctly treated as an imbalance.
         */
        env.flags |= LBF_ALL_PINNED;
        env.loop_max  = min(sysctl_sched_nr_migrate, busiest->nr_running);

more_balance:
        raw_spin_lock_irqsave(&busiest->lock, flags);

        /*
         * cur_ld_moved - load moved in current iteration
         * ld_moved     - cumulative load moved across iterations
         */
        cur_ld_moved = detach_tasks(&env);

        /*
         * We've detached some tasks from busiest_rq. Every
         * task is masked "TASK_ON_RQ_MIGRATING", so we can safely
         * unlock busiest->lock, and we are able to be sure
         * that nobody can manipulate the tasks in parallel.
         * See task_rq_lock() family for the details.
         */

        raw_spin_unlock(&busiest->lock);

        if (cur_ld_moved) {
            attach_tasks(&env);
            ld_moved += cur_ld_moved;
        }

        local_irq_restore(flags);

        if (env.flags & LBF_NEED_BREAK) {
            env.flags &= ~LBF_NEED_BREAK;
            goto more_balance;
        }

        /*
         * Revisit (affine) tasks on src_cpu that couldn't be moved to
         * us and move them to an alternate dst_cpu in our sched_group
         * where they can run. The upper limit on how many times we
         * iterate on same src_cpu is dependent on number of cpus in our
         * sched_group.
         *
         * This changes load balance semantics a bit on who can move
         * load to a given_cpu. In addition to the given_cpu itself
         * (or a ilb_cpu acting on its behalf where given_cpu is
         * nohz-idle), we now have balance_cpu in a position to move
         * load to given_cpu. In rare situations, this may cause
         * conflicts (balance_cpu and given_cpu/ilb_cpu deciding
         * _independently_ and at _same_ time to move some load to
         * given_cpu) causing exceess load to be moved to given_cpu.
         * This however should not happen so much in practice and
         * moreover subsequent load balance cycles should correct the
         * excess load moved.
         */
        if ((env.flags & LBF_DST_PINNED) && env.imbalance > 0) {

            /* Prevent to re-select dst_cpu via env's cpus */
            cpumask_clear_cpu(env.dst_cpu, env.cpus);

            env.dst_rq       = cpu_rq(env.new_dst_cpu);
            env.dst_cpu      = env.new_dst_cpu;
            env.flags       &= ~LBF_DST_PINNED;
            env.loop     = 0;
            env.loop_break   = sched_nr_migrate_break;

            /*
             * Go back to "more_balance" rather than "redo" since we
             * need to continue with same src_cpu.
             */
            goto more_balance;
        }

        /*
         * We failed to reach balance because of affinity.
         */
        if (sd_parent) {
            int *group_imbalance = &sd_parent->groups->sgc->imbalance;

            if ((env.flags & LBF_SOME_PINNED) && env.imbalance > 0)
                *group_imbalance = 1;
        }

        /* All tasks on this runqueue were pinned by CPU affinity */
        if (unlikely(env.flags & LBF_ALL_PINNED)) {
            cpumask_clear_cpu(cpu_of(busiest), cpus);
            if (!cpumask_empty(cpus)) {
                env.loop = 0;
                env.loop_break = sched_nr_migrate_break;
                goto redo;
            }
            goto out_all_pinned;
        }
    }

    if (!ld_moved) {
        schedstat_inc(sd, lb_failed[idle]);
        /*
         * Increment the failure counter only on periodic balance.
         * We do not want newidle balance, which can be very
         * frequent, pollute the failure counter causing
         * excessive cache_hot migrations and active balances.
         */
        if (idle != CPU_NEWLY_IDLE)
            sd->nr_balance_failed++;

        if (need_active_balance(&env)) {
            raw_spin_lock_irqsave(&busiest->lock, flags);

            /* don't kick the active_load_balance_cpu_stop,
             * if the curr task on busiest cpu can't be
             * moved to this_cpu
             */
            if (!cpumask_test_cpu(this_cpu,
                    tsk_cpus_allowed(busiest->curr))) {
                raw_spin_unlock_irqrestore(&busiest->lock,
                                flags);
                env.flags |= LBF_ALL_PINNED;
                goto out_one_pinned;
            }

            /*
             * ->active_balance synchronizes accesses to
             * ->active_balance_work.  Once set, it's cleared
             * only after active load balance is finished.
             */
            if (!busiest->active_balance) {
                busiest->active_balance = 1;
                busiest->push_cpu = this_cpu;
                active_balance = 1;
            }
            raw_spin_unlock_irqrestore(&busiest->lock, flags);

            if (active_balance) {
                stop_one_cpu_nowait(cpu_of(busiest),
                    active_load_balance_cpu_stop, busiest,
                    &busiest->active_balance_work);
            }

            /*
             * We've kicked active balancing, reset the failure
             * counter.
             */
            sd->nr_balance_failed = sd->cache_nice_tries+1;
        }
    } else
        sd->nr_balance_failed = 0;

    if (likely(!active_balance)) {
        /* We were unbalanced, so reset the balancing interval */
        sd->balance_interval = sd->min_interval;
    } else {
        /*
         * If we've begun active balancing, start to back off. This
         * case may not be covered by the all_pinned logic if there
         * is only 1 task on the busy runqueue (because we don't call
         * detach_tasks).
         */
        if (sd->balance_interval < sd->max_interval)
            sd->balance_interval *= 2;
    }

    goto out;

out_balanced:
    /*
     * We reach balance although we may have faced some affinity
     * constraints. Clear the imbalance flag if it was set.
     */
    if (sd_parent) {
        int *group_imbalance = &sd_parent->groups->sgc->imbalance;

        if (*group_imbalance)
            *group_imbalance = 0;
    }

out_all_pinned:
    /*
     * We reach balance because all tasks are pinned at this level so
     * we can't migrate them. Let the imbalance flag set so parent level
     * can try to migrate them.
     */
    schedstat_inc(sd, lb_balanced[idle]);

    sd->nr_balance_failed = 0;

out_one_pinned:
    /* tune up the balancing interval */
    if (((env.flags & LBF_ALL_PINNED) &&
            sd->balance_interval < MAX_PINNED_INTERVAL) ||
            (sd->balance_interval < sd->max_interval))
        sd->balance_interval *= 2;

    ld_moved = 0;
out:
    return ld_moved;
}

static inline unsigned long
get_sd_balance_interval(struct sched_domain *sd, int cpu_busy)
{
    unsigned long interval = sd->balance_interval;

    if (cpu_busy)
        interval *= sd->busy_factor;

    /* scale ms to jiffies */
    interval = msecs_to_jiffies(interval);
    interval = clamp(interval, 1UL, max_load_balance_interval);

    return interval;
}

static inline void
update_next_balance(struct sched_domain *sd, int cpu_busy, unsigned long *next_balance)
{
    unsigned long interval, next;

    interval = get_sd_balance_interval(sd, cpu_busy);
    next = sd->last_balance + interval;

    if (time_after(*next_balance, next))
        *next_balance = next;
}

/*
 * idle_balance is called by schedule() if this_cpu is about to become
 * idle. Attempts to pull tasks from other CPUs.
 */
static int idle_balance(struct rq *this_rq)
{
    unsigned long next_balance = jiffies + HZ;
    int this_cpu = this_rq->cpu;
    struct sched_domain *sd;
    int pulled_task = 0;
    u64 curr_cost = 0;

    /*
     * We must set idle_stamp _before_ calling idle_balance(), such that we
     * measure the duration of idle_balance() as idle time.
     */
    this_rq->idle_stamp = rq_clock(this_rq);

    if (this_rq->avg_idle < sysctl_sched_migration_cost ||
        !this_rq->rd->overload) {
        rcu_read_lock();
        sd = rcu_dereference_check_sched_domain(this_rq->sd);
        if (sd)
            update_next_balance(sd, 0, &next_balance);
        rcu_read_unlock();

        goto out;
    }

    raw_spin_unlock(&this_rq->lock);

    update_blocked_averages(this_cpu);
    rcu_read_lock();
    for_each_domain(this_cpu, sd) {
        int continue_balancing = 1;
        u64 t0, domain_cost;

        if (!(sd->flags & SD_LOAD_BALANCE))
            continue;

        if (this_rq->avg_idle < curr_cost + sd->max_newidle_lb_cost) {
            update_next_balance(sd, 0, &next_balance);
            break;
        }

        if (sd->flags & SD_BALANCE_NEWIDLE) {
            t0 = sched_clock_cpu(this_cpu);

            pulled_task = load_balance(this_cpu, this_rq,
                           sd, CPU_NEWLY_IDLE,
                           &continue_balancing);

            domain_cost = sched_clock_cpu(this_cpu) - t0;
            if (domain_cost > sd->max_newidle_lb_cost)
                sd->max_newidle_lb_cost = domain_cost;

            curr_cost += domain_cost;
        }

        update_next_balance(sd, 0, &next_balance);

        /*
         * Stop searching for tasks to pull if there are
         * now runnable tasks on this rq.
         */
        if (pulled_task || this_rq->nr_running > 0)
            break;
    }
    rcu_read_unlock();

    raw_spin_lock(&this_rq->lock);

    if (curr_cost > this_rq->max_idle_balance_cost)
        this_rq->max_idle_balance_cost = curr_cost;

    /*
     * While browsing the domains, we released the rq lock, a task could
     * have been enqueued in the meantime. Since we're not going idle,
     * pretend we pulled a task.
     */
    if (this_rq->cfs.h_nr_running && !pulled_task)
        pulled_task = 1;

out:
    /* Move the next balance forward */
    if (time_after(this_rq->next_balance, next_balance))
        this_rq->next_balance = next_balance;

    /* Is there a task of a high priority class? */
    if (this_rq->nr_running != this_rq->cfs.h_nr_running)
        pulled_task = -1;

    if (pulled_task)
        this_rq->idle_stamp = 0;

    return pulled_task;
}

/*
 * active_load_balance_cpu_stop is run by cpu stopper. It pushes
 * running tasks off the busiest CPU onto idle CPUs. It requires at
 * least 1 task to be running on each physical CPU where possible, and
 * avoids physical / logical imbalances.
 */
static int active_load_balance_cpu_stop(void *data)
{
    struct rq *busiest_rq = data;
    int busiest_cpu = cpu_of(busiest_rq);
    int target_cpu = busiest_rq->push_cpu;
    struct rq *target_rq = cpu_rq(target_cpu);
    struct sched_domain *sd;
    struct task_struct *p = NULL;

    raw_spin_lock_irq(&busiest_rq->lock);

    /* make sure the requested cpu hasn't gone down in the meantime */
    if (unlikely(busiest_cpu != smp_processor_id() ||
             !busiest_rq->active_balance))
        goto out_unlock;

    /* Is there any task to move? */
    if (busiest_rq->nr_running <= 1)
        goto out_unlock;

    /*
     * This condition is "impossible", if it occurs
     * we need to fix it. Originally reported by
     * Bjorn Helgaas on a 128-cpu setup.
     */
    BUG_ON(busiest_rq == target_rq);

    /* Search for an sd spanning us and the target CPU. */
    rcu_read_lock();
    for_each_domain(target_cpu, sd) {
        if ((sd->flags & SD_LOAD_BALANCE) &&
            cpumask_test_cpu(busiest_cpu, sched_domain_span(sd)))
                break;
    }

    if (likely(sd)) {
        struct lb_env env = {
            .sd         = sd,
            .dst_cpu    = target_cpu,
            .dst_rq     = target_rq,
            .src_cpu    = busiest_rq->cpu,
            .src_rq     = busiest_rq,
            .idle       = CPU_IDLE,
        };

        schedstat_inc(sd, alb_count);

        p = detach_one_task(&env);
        if (p)
            schedstat_inc(sd, alb_pushed);
        else
            schedstat_inc(sd, alb_failed);
    }
    rcu_read_unlock();
out_unlock:
    busiest_rq->active_balance = 0;
    raw_spin_unlock(&busiest_rq->lock);

    if (p)
        attach_one_task(target_rq, p);

    local_irq_enable();

    return 0;
}

static inline int on_null_domain(struct rq *rq)
{
    return unlikely(!rcu_dereference_sched(rq->sd));
}

#ifdef CONFIG_NO_HZ_COMMON
/*
 * idle load balancing details
 * - When one of the busy CPUs notice that there may be an idle rebalancing
 *   needed, they will kick the idle load balancer, which then does idle
 *   load balancing for all the idle CPUs.
 */
static struct {
    cpumask_var_t idle_cpus_mask;
    atomic_t nr_cpus;
    unsigned long next_balance;     /* in jiffy units */
} nohz ____cacheline_aligned;

static inline int find_new_ilb(void)
{
    int ilb = cpumask_first(nohz.idle_cpus_mask);

    if (ilb < nr_cpu_ids && idle_cpu(ilb))
        return ilb;

    return nr_cpu_ids;
}

/*
 * Kick a CPU to do the nohz balancing, if it is time for it. We pick the
 * nohz_load_balancer CPU (if there is one) otherwise fallback to any idle
 * CPU (if there is one).
 */
static void nohz_balancer_kick(void)
{
    int ilb_cpu;

    nohz.next_balance++;

    ilb_cpu = find_new_ilb();

    if (ilb_cpu >= nr_cpu_ids)
        return;

    if (test_and_set_bit(NOHZ_BALANCE_KICK, nohz_flags(ilb_cpu)))
        return;
    /*
     * Use smp_send_reschedule() instead of resched_cpu().
     * This way we generate a sched IPI on the target cpu which
     * is idle. And the softirq performing nohz idle load balance
     * will be run before returning from the IPI.
     */
    smp_send_reschedule(ilb_cpu);
    return;
}

static inline void nohz_balance_exit_idle(int cpu)
{
    if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))) {
        /*
         * Completely isolated CPUs don't ever set, so we must test.
         */
        if (likely(cpumask_test_cpu(cpu, nohz.idle_cpus_mask))) {
            cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
            atomic_dec(&nohz.nr_cpus);
        }
        clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
    }
}

static inline void set_cpu_sd_state_busy(void)
{
    struct sched_domain *sd;
    int cpu = smp_processor_id();

    rcu_read_lock();
    sd = rcu_dereference(per_cpu(sd_busy, cpu));

    if (!sd || !sd->nohz_idle)
        goto unlock;
    sd->nohz_idle = 0;

    atomic_inc(&sd->groups->sgc->nr_busy_cpus);
unlock:
    rcu_read_unlock();
}

void set_cpu_sd_state_idle(void)
{
    struct sched_domain *sd;
    int cpu = smp_processor_id();

    rcu_read_lock();
    sd = rcu_dereference(per_cpu(sd_busy, cpu));

    if (!sd || sd->nohz_idle)
        goto unlock;
    sd->nohz_idle = 1;

    atomic_dec(&sd->groups->sgc->nr_busy_cpus);
unlock:
    rcu_read_unlock();
}

/*
 * This routine will record that the cpu is going idle with tick stopped.
 * This info will be used in performing idle load balancing in the future.
 */
void nohz_balance_enter_idle(int cpu)
{
    /*
     * If this cpu is going down, then nothing needs to be done.
     */
    if (!cpu_active(cpu))
        return;

    if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))
        return;

    /*
     * If we're a completely isolated CPU, we don't play.
     */
    if (on_null_domain(cpu_rq(cpu)))
        return;

    cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
    atomic_inc(&nohz.nr_cpus);
    set_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
}

static int sched_ilb_notifier(struct notifier_block *nfb,
                    unsigned long action, void *hcpu)
{
    switch (action & ~CPU_TASKS_FROZEN) {
    case CPU_DYING:
        nohz_balance_exit_idle(smp_processor_id());
        return NOTIFY_OK;
    default:
        return NOTIFY_DONE;
    }
}
#endif

static DEFINE_SPINLOCK(balancing);

/*
 * Scale the max load_balance interval with the number of CPUs in the system.
 * This trades load-balance latency on larger machines for less cross talk.
 */
void update_max_interval(void)
{
    max_load_balance_interval = HZ*num_online_cpus()/10;
}

/*
 * It checks each scheduling domain to see if it is due to be balanced,
 * and initiates a balancing operation if so.
 *
 * Balancing parameters are set up in init_sched_domains.
 */
static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle)
{
    int continue_balancing = 1;
    int cpu = rq->cpu;
    unsigned long interval;
    struct sched_domain *sd;
    /* Earliest time when we have to do rebalance again */
    unsigned long next_balance = jiffies + 60*HZ;
    int update_next_balance = 0;
    int need_serialize, need_decay = 0;
    u64 max_cost = 0;

    update_blocked_averages(cpu);

    rcu_read_lock();
    for_each_domain(cpu, sd) {
        /*
         * Decay the newidle max times here because this is a regular
         * visit to all the domains. Decay ~1% per second.
         */
        if (time_after(jiffies, sd->next_decay_max_lb_cost)) {
            sd->max_newidle_lb_cost =
                (sd->max_newidle_lb_cost * 253) / 256;
            sd->next_decay_max_lb_cost = jiffies + HZ;
            need_decay = 1;
        }
        max_cost += sd->max_newidle_lb_cost;

        if (!(sd->flags & SD_LOAD_BALANCE))
            continue;

        /*
         * Stop the load balance at this level. There is another
         * CPU in our sched group which is doing load balancing more
         * actively.
         */
        if (!continue_balancing) {
            if (need_decay)
                continue;
            break;
        }

        interval = get_sd_balance_interval(sd, idle != CPU_IDLE);

        need_serialize = sd->flags & SD_SERIALIZE;
        if (need_serialize) {
            if (!spin_trylock(&balancing))
                goto out;
        }

        if (time_after_eq(jiffies, sd->last_balance + interval)) {
            if (load_balance(cpu, rq, sd, idle, &continue_balancing)) {
                /*
                 * The LBF_DST_PINNED logic could have changed
                 * env->dst_cpu, so we can't know our idle
                 * state even if we migrated tasks. Update it.
                 */
                idle = idle_cpu(cpu) ? CPU_IDLE : CPU_NOT_IDLE;
            }
            sd->last_balance = jiffies;
            interval = get_sd_balance_interval(sd, idle != CPU_IDLE);
        }
        if (need_serialize)
            spin_unlock(&balancing);
out:
        if (time_after(next_balance, sd->last_balance + interval)) {
            next_balance = sd->last_balance + interval;
            update_next_balance = 1;
        }
    }
    if (need_decay) {
        /*
         * Ensure the rq-wide value also decays but keep it at a
         * reasonable floor to avoid funnies with rq->avg_idle.
         */
        rq->max_idle_balance_cost =
            max((u64)sysctl_sched_migration_cost, max_cost);
    }
    rcu_read_unlock();

    /*
     * next_balance will be updated only when there is a need.
     * When the cpu is attached to null domain for ex, it will not be
     * updated.
     */
    if (likely(update_next_balance)) {
        rq->next_balance = next_balance;

#ifdef CONFIG_NO_HZ_COMMON
        /*
         * If this CPU has been elected to perform the nohz idle
         * balance. Other idle CPUs have already rebalanced with
         * nohz_idle_balance() and nohz.next_balance has been
         * updated accordingly. This CPU is now running the idle load
         * balance for itself and we need to update the
         * nohz.next_balance accordingly.
         */
        if ((idle == CPU_IDLE) && time_after(nohz.next_balance, rq->next_balance))
            nohz.next_balance = rq->next_balance;
#endif
    }
}

#ifdef CONFIG_NO_HZ_COMMON
/*
 * In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the
 * rebalancing for all the cpus for whom scheduler ticks are stopped.
 */
static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
{
    int this_cpu = this_rq->cpu;
    struct rq *rq;
    int balance_cpu;
    /* Earliest time when we have to do rebalance again */
    unsigned long next_balance = jiffies + 60*HZ;
    int update_next_balance = 0;

    if (idle != CPU_IDLE ||
        !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)))
        goto end;

    for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
        if (balance_cpu == this_cpu || !idle_cpu(balance_cpu))
            continue;

        /*
         * If this cpu gets work to do, stop the load balancing
         * work being done for other cpus. Next load
         * balancing owner will pick it up.
         */
        if (need_resched())
            break;

        rq = cpu_rq(balance_cpu);

        /*
         * If time for next balance is due,
         * do the balance.
         */
        if (time_after_eq(jiffies, rq->next_balance)) {
            raw_spin_lock_irq(&rq->lock);
            update_rq_clock(rq);
            update_cpu_load_idle(rq);
            raw_spin_unlock_irq(&rq->lock);
            rebalance_domains(rq, CPU_IDLE);
        }

        if (time_after(next_balance, rq->next_balance)) {
            next_balance = rq->next_balance;
            update_next_balance = 1;
        }
    }

    /*
     * next_balance will be updated only when there is a need.
     * When the CPU is attached to null domain for ex, it will not be
     * updated.
     */
    if (likely(update_next_balance))
        nohz.next_balance = next_balance;
end:
    clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
}

/*
 * Current heuristic for kicking the idle load balancer in the presence
 * of an idle cpu in the system.
 *   - This rq has more than one task.
 *   - This rq has at least one CFS task and the capacity of the CPU is
 *     significantly reduced because of RT tasks or IRQs.
 *   - At parent of LLC scheduler domain level, this cpu's scheduler group has
 *     multiple busy cpu.
 *   - For SD_ASYM_PACKING, if the lower numbered cpu's in the scheduler
 *     domain span are idle.
 */
static inline bool nohz_kick_needed(struct rq *rq)
{
    unsigned long now = jiffies;
    struct sched_domain *sd;
    struct sched_group_capacity *sgc;
    int nr_busy, cpu = rq->cpu;
    bool kick = false;

    if (unlikely(rq->idle_balance))
        return false;

       /*
    * We may be recently in ticked or tickless idle mode. At the first
    * busy tick after returning from idle, we will update the busy stats.
    */
    set_cpu_sd_state_busy();
    nohz_balance_exit_idle(cpu);

    /*
     * None are in tickless mode and hence no need for NOHZ idle load
     * balancing.
     */
    if (likely(!atomic_read(&nohz.nr_cpus)))
        return false;

    if (time_before(now, nohz.next_balance))
        return false;

    if (rq->nr_running >= 2)
        return true;

    rcu_read_lock();
    sd = rcu_dereference(per_cpu(sd_busy, cpu));
    if (sd) {
        sgc = sd->groups->sgc;
        nr_busy = atomic_read(&sgc->nr_busy_cpus);

        if (nr_busy > 1) {
            kick = true;
            goto unlock;
        }

    }

    sd = rcu_dereference(rq->sd);
    if (sd) {
        if ((rq->cfs.h_nr_running >= 1) &&
                check_cpu_capacity(rq, sd)) {
            kick = true;
            goto unlock;
        }
    }

    sd = rcu_dereference(per_cpu(sd_asym, cpu));
    if (sd && (cpumask_first_and(nohz.idle_cpus_mask,
                  sched_domain_span(sd)) < cpu)) {
        kick = true;
        goto unlock;
    }

unlock:
    rcu_read_unlock();
    return kick;
}
#else
static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) { }
#endif

/*
 * run_rebalance_domains is triggered when needed from the scheduler tick.
 * Also triggered for nohz idle balancing (with nohz_balancing_kick set).
 */
static void run_rebalance_domains(struct softirq_action *h)
{
    struct rq *this_rq = this_rq();
    enum cpu_idle_type idle = this_rq->idle_balance ?
                        CPU_IDLE : CPU_NOT_IDLE;

    /*
     * If this cpu has a pending nohz_balance_kick, then do the
     * balancing on behalf of the other idle cpus whose ticks are
     * stopped. Do nohz_idle_balance *before* rebalance_domains to
     * give the idle cpus a chance to load balance. Else we may
     * load balance only within the local sched_domain hierarchy
     * and abort nohz_idle_balance altogether if we pull some load.
     */
    nohz_idle_balance(this_rq, idle);
    rebalance_domains(this_rq, idle);
}

/*
 * Trigger the SCHED_SOFTIRQ if it is time to do periodic load balancing.
 */
void trigger_load_balance(struct rq *rq)
{
    /* Don't need to rebalance while attached to NULL domain */
    if (unlikely(on_null_domain(rq)))
        return;

    if (time_after_eq(jiffies, rq->next_balance))
        raise_softirq(SCHED_SOFTIRQ);
#ifdef CONFIG_NO_HZ_COMMON
    if (nohz_kick_needed(rq))
        nohz_balancer_kick();
#endif
}

static void rq_online_fair(struct rq *rq)
{
    update_sysctl();

    update_runtime_enabled(rq);
}

static void rq_offline_fair(struct rq *rq)
{
    update_sysctl();

    /* Ensure any throttled groups are reachable by pick_next_task */
    unthrottle_offline_cfs_rqs(rq);
}

#endif /* CONFIG_SMP */

/*
 * scheduler tick hitting a task of our scheduling class:
 */
static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
{
    struct cfs_rq *cfs_rq;
    /*  获取到当前进程curr所在的调度实体  */
    struct sched_entity *se = &curr->se;

    /* for_each_sched_entity
     * 在不支持组调度条件下, 只循环一次
     * 在组调度的条件下, 调度实体存在层次关系, 
     * 更新子调度实体的同时必须更新父调度实体  */
    for_each_sched_entity(se)
    {
        /*  获取当当前运行的进程所在的CFS就绪队列  */
        cfs_rq = cfs_rq_of(se);
        /*  完成周期性调度  */
        entity_tick(cfs_rq, se, queued);
    }

    if (static_branch_unlikely(&sched_numa_balancing))
        task_tick_numa(rq, curr);
}

/*
 * called on fork with the child task as argument from the parent's context
 *  - child not yet on the tasklist
 *  - preemption disabled
 */
static void task_fork_fair(struct task_struct *p)
{
    struct cfs_rq *cfs_rq;
    struct sched_entity *se = &p->se, *curr;
    int this_cpu = smp_processor_id();
    struct rq *rq = this_rq();
    unsigned long flags;

    raw_spin_lock_irqsave(&rq->lock, flags);

    update_rq_clock(rq);

    cfs_rq = task_cfs_rq(current);
    curr = cfs_rq->curr;

    /*
     * Not only the cpu but also the task_group of the parent might have
     * been changed after parent->se.parent,cfs_rq were copied to
     * child->se.parent,cfs_rq. So call __set_task_cpu() to make those
     * of child point to valid ones.
     */
    rcu_read_lock();
    __set_task_cpu(p, this_cpu);
    rcu_read_unlock();

    update_curr(cfs_rq);

    if (curr)
        se->vruntime = curr->vruntime;
    place_entity(cfs_rq, se, 1);

    if (sysctl_sched_child_runs_first && curr && entity_before(curr, se)) {
        /*
         * Upon rescheduling, sched_class::put_prev_task() will place
         * 'current' within the tree based on its new key value.
         */
        swap(curr->vruntime, se->vruntime);
        resched_curr(rq);
    }

    se->vruntime -= cfs_rq->min_vruntime;

    raw_spin_unlock_irqrestore(&rq->lock, flags);
}

/*
 * Priority of the task has changed. Check to see if we preempt
 * the current task.
 */
static void
prio_changed_fair(struct rq *rq, struct task_struct *p, int oldprio)
{
    if (!task_on_rq_queued(p))
        return;

    /*
     * Reschedule if we are currently running on this runqueue and
     * our priority decreased, or if we are not currently running on
     * this runqueue and our priority is higher than the current's
     */
    if (rq->curr == p) {
        if (p->prio > oldprio)
            resched_curr(rq);
    } else
        check_preempt_curr(rq, p, 0);
}

static inline bool vruntime_normalized(struct task_struct *p)
{
    struct sched_entity *se = &p->se;

    /*
     * In both the TASK_ON_RQ_QUEUED and TASK_ON_RQ_MIGRATING cases,
     * the dequeue_entity(.flags=0) will already have normalized the
     * vruntime.
     */
    if (p->on_rq)
        return true;

    /*
     * When !on_rq, vruntime of the task has usually NOT been normalized.
     * But there are some cases where it has already been normalized:
     *
     * - A forked child which is waiting for being woken up by
     *   wake_up_new_task().
     * - A task which has been woken up by try_to_wake_up() and
     *   waiting for actually being woken up by sched_ttwu_pending().
     */
    if (!se->sum_exec_runtime || p->state == TASK_WAKING)
        return true;

    return false;
}

static void detach_task_cfs_rq(struct task_struct *p)
{
    struct sched_entity *se = &p->se;
    struct cfs_rq *cfs_rq = cfs_rq_of(se);

    if (!vruntime_normalized(p)) {
        /*
         * Fix up our vruntime so that the current sleep doesn't
         * cause 'unlimited' sleep bonus.
         */
        place_entity(cfs_rq, se, 0);
        se->vruntime -= cfs_rq->min_vruntime;
    }

    /* Catch up with the cfs_rq and remove our load when we leave */
    detach_entity_load_avg(cfs_rq, se);
}

static void attach_task_cfs_rq(struct task_struct *p)
{
    struct sched_entity *se = &p->se;
    struct cfs_rq *cfs_rq = cfs_rq_of(se);

#ifdef CONFIG_FAIR_GROUP_SCHED
    /*
     * Since the real-depth could have been changed (only FAIR
     * class maintain depth value), reset depth properly.
     */
    se->depth = se->parent ? se->parent->depth + 1 : 0;
#endif

    /* Synchronize task with its cfs_rq */
    attach_entity_load_avg(cfs_rq, se);

    if (!vruntime_normalized(p))
        se->vruntime += cfs_rq->min_vruntime;
}

static void switched_from_fair(struct rq *rq, struct task_struct *p)
{
    detach_task_cfs_rq(p);
}

static void switched_to_fair(struct rq *rq, struct task_struct *p)
{
    attach_task_cfs_rq(p);

    if (task_on_rq_queued(p)) {
        /*
         * We were most likely switched from sched_rt, so
         * kick off the schedule if running, otherwise just see
         * if we can still preempt the current task.
         */
        if (rq->curr == p)
            resched_curr(rq);
        else
            check_preempt_curr(rq, p, 0);
    }
}

/* Account for a task changing its policy or group.
 *
 * This routine is mostly called to set cfs_rq->curr field when a task
 * migrates between groups/classes.
 */
static void set_curr_task_fair(struct rq *rq)
{
    struct sched_entity *se = &rq->curr->se;

    for_each_sched_entity(se) {
        struct cfs_rq *cfs_rq = cfs_rq_of(se);

        set_next_entity(cfs_rq, se);
        /* ensure bandwidth has been allocated on our new cfs_rq */
        account_cfs_rq_runtime(cfs_rq, 0);
    }
}

void init_cfs_rq(struct cfs_rq *cfs_rq)
{
    cfs_rq->tasks_timeline = RB_ROOT;
    cfs_rq->min_vruntime = (u64)(-(1LL << 20));
#ifndef CONFIG_64BIT
    cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
#endif
#ifdef CONFIG_SMP
    atomic_long_set(&cfs_rq->removed_load_avg, 0);
    atomic_long_set(&cfs_rq->removed_util_avg, 0);
#endif
}

#ifdef CONFIG_FAIR_GROUP_SCHED
static void task_move_group_fair(struct task_struct *p)
{
    detach_task_cfs_rq(p);
    set_task_rq(p, task_cpu(p));

#ifdef CONFIG_SMP
    /* Tell se's cfs_rq has been changed -- migrated */
    p->se.avg.last_update_time = 0;
#endif
    attach_task_cfs_rq(p);
}

void free_fair_sched_group(struct task_group *tg)
{
    int i;

    destroy_cfs_bandwidth(tg_cfs_bandwidth(tg));

    for_each_possible_cpu(i) {
        if (tg->cfs_rq)
            kfree(tg->cfs_rq[i]);
        if (tg->se)
            kfree(tg->se[i]);
    }

    kfree(tg->cfs_rq);
    kfree(tg->se);
}

int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent)
{
    struct cfs_rq *cfs_rq;
    struct sched_entity *se;
    int i;

    tg->cfs_rq = kzalloc(sizeof(cfs_rq) * nr_cpu_ids, GFP_KERNEL);
    if (!tg->cfs_rq)
        goto err;
    tg->se = kzalloc(sizeof(se) * nr_cpu_ids, GFP_KERNEL);
    if (!tg->se)
        goto err;

    tg->shares = NICE_0_LOAD;

    init_cfs_bandwidth(tg_cfs_bandwidth(tg));

    for_each_possible_cpu(i) {
        cfs_rq = kzalloc_node(sizeof(struct cfs_rq),
                      GFP_KERNEL, cpu_to_node(i));
        if (!cfs_rq)
            goto err;

        se = kzalloc_node(sizeof(struct sched_entity),
                  GFP_KERNEL, cpu_to_node(i));
        if (!se)
            goto err_free_rq;

        init_cfs_rq(cfs_rq);
        init_tg_cfs_entry(tg, cfs_rq, se, i, parent->se[i]);
        init_entity_runnable_average(se);
    }

    return 1;

err_free_rq:
    kfree(cfs_rq);
err:
    return 0;
}

void unregister_fair_sched_group(struct task_group *tg)
{
    unsigned long flags;
    struct rq *rq;
    int cpu;

    for_each_possible_cpu(cpu) {
        if (tg->se[cpu])
            remove_entity_load_avg(tg->se[cpu]);

        /*
         * Only empty task groups can be destroyed; so we can speculatively
         * check on_list without danger of it being re-added.
         */
        if (!tg->cfs_rq[cpu]->on_list)
            continue;

        rq = cpu_rq(cpu);

        raw_spin_lock_irqsave(&rq->lock, flags);
        list_del_leaf_cfs_rq(tg->cfs_rq[cpu]);
        raw_spin_unlock_irqrestore(&rq->lock, flags);
    }
}

void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
            struct sched_entity *se, int cpu,
            struct sched_entity *parent)
{
    struct rq *rq = cpu_rq(cpu);

    cfs_rq->tg = tg;
    cfs_rq->rq = rq;
    init_cfs_rq_runtime(cfs_rq);

    tg->cfs_rq[cpu] = cfs_rq;
    tg->se[cpu] = se;

    /* se could be NULL for root_task_group */
    if (!se)
        return;

    if (!parent) {
        se->cfs_rq = &rq->cfs;
        se->depth = 0;
    } else {
        se->cfs_rq = parent->my_q;
        se->depth = parent->depth + 1;
    }

    se->my_q = cfs_rq;
    /* guarantee group entities always have weight */
    update_load_set(&se->load, NICE_0_LOAD);
    se->parent = parent;
}

static DEFINE_MUTEX(shares_mutex);

int sched_group_set_shares(struct task_group *tg, unsigned long shares)
{
    int i;
    unsigned long flags;

    /*
     * We can't change the weight of the root cgroup.
     */
    if (!tg->se[0])
        return -EINVAL;

    shares = clamp(shares, scale_load(MIN_SHARES), scale_load(MAX_SHARES));

    mutex_lock(&shares_mutex);
    if (tg->shares == shares)
        goto done;

    tg->shares = shares;
    for_each_possible_cpu(i) {
        struct rq *rq = cpu_rq(i);
        struct sched_entity *se;

        se = tg->se[i];
        /* Propagate contribution to hierarchy */
        raw_spin_lock_irqsave(&rq->lock, flags);

        /* Possible calls to update_curr() need rq clock */
        update_rq_clock(rq);
        for_each_sched_entity(se)
            update_cfs_shares(group_cfs_rq(se));
        raw_spin_unlock_irqrestore(&rq->lock, flags);
    }

done:
    mutex_unlock(&shares_mutex);
    return 0;
}
#else /* CONFIG_FAIR_GROUP_SCHED */

void free_fair_sched_group(struct task_group *tg) { }

int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent)
{
    return 1;
}

void unregister_fair_sched_group(struct task_group *tg) { }

#endif /* CONFIG_FAIR_GROUP_SCHED */


static unsigned int get_rr_interval_fair(struct rq *rq, struct task_struct *task)
{
    struct sched_entity *se = &task->se;
    unsigned int rr_interval = 0;

    /*
     * Time slice is 0 for SCHED_OTHER tasks that are on an otherwise
     * idle runqueue:
     */
    if (rq->cfs.load.weight)
        rr_interval = NS_TO_JIFFIES(sched_slice(cfs_rq_of(se), se));

    return rr_interval;
}

/*
 * All the scheduling class methods:
 */
const struct sched_class fair_sched_class = {
    .next           = &idle_sched_class,  /*  下个优先级的调度类, 所有的调度类通过next链接在一个链表中*/
    .enqueue_task       = enqueue_task_fair,
    .dequeue_task       = dequeue_task_fair,
    .yield_task         = yield_task_fair,
    .yield_to_task      = yield_to_task_fair,

    .check_preempt_curr     = check_preempt_wakeup,

    .pick_next_task     = pick_next_task_fair,
    .put_prev_task      = put_prev_task_fair,

#ifdef CONFIG_SMP
    .select_task_rq     = select_task_rq_fair,
    .migrate_task_rq    = migrate_task_rq_fair,

    .rq_online          = rq_online_fair,
    .rq_offline         = rq_offline_fair,

    .task_waking        = task_waking_fair,
    .task_dead          = task_dead_fair,
    .set_cpus_allowed       = set_cpus_allowed_common,
#endif

    .set_curr_task      = set_curr_task_fair,
    .task_tick          = task_tick_fair,
    .task_fork          = task_fork_fair,

    .prio_changed       = prio_changed_fair,
    .switched_from      = switched_from_fair,
    .switched_to        = switched_to_fair,

    .get_rr_interval    = get_rr_interval_fair,

    .update_curr        = update_curr_fair,

#ifdef CONFIG_FAIR_GROUP_SCHED
    .task_move_group    = task_move_group_fair,
#endif
};

#ifdef CONFIG_SCHED_DEBUG
void print_cfs_stats(struct seq_file *m, int cpu)
{
    struct cfs_rq *cfs_rq;

    rcu_read_lock();
    for_each_leaf_cfs_rq(cpu_rq(cpu), cfs_rq)
        print_cfs_rq(m, cpu, cfs_rq);
    rcu_read_unlock();
}

#ifdef CONFIG_NUMA_BALANCING
void show_numa_stats(struct task_struct *p, struct seq_file *m)
{
    int node;
    unsigned long tsf = 0, tpf = 0, gsf = 0, gpf = 0;

    for_each_online_node(node) {
        if (p->numa_faults) {
            tsf = p->numa_faults[task_faults_idx(NUMA_MEM, node, 0)];
            tpf = p->numa_faults[task_faults_idx(NUMA_MEM, node, 1)];
        }
        if (p->numa_group) {
            gsf = p->numa_group->faults[task_faults_idx(NUMA_MEM, node, 0)],
            gpf = p->numa_group->faults[task_faults_idx(NUMA_MEM, node, 1)];
        }
        print_numa_stats(m, node, tsf, tpf, gsf, gpf);
    }
}
#endif /* CONFIG_NUMA_BALANCING */
#endif /* CONFIG_SCHED_DEBUG */

__init void init_sched_fair_class(void)
{
#ifdef CONFIG_SMP
    open_softirq(SCHED_SOFTIRQ, run_rebalance_domains);

#ifdef CONFIG_NO_HZ_COMMON
    nohz.next_balance = jiffies;
    zalloc_cpumask_var(&nohz.idle_cpus_mask, GFP_NOWAIT);
    cpu_notifier(sched_ilb_notifier, 0);
#endif
#endif /* SMP */

}


